Effects of hypothyroidism on the mesenteric and omental adipose tissue in rats

To characterize the influence of hypothyroidism on the endocrine activity of mesenteric and omental adipose tissue (MOAT) and the peripheral regulation of energy balance (EB) in rats, we analyzed food intake (FI); basal metabolic rate (BMR); locomotor activity; body weight (BW); serum hormone concentrations and the expression of their receptors in MOAT. We evaluated the morphology and differentiation of adipocytes. Hypothyroidism decreased FI, BMR and BW. The percentage of visceral white adipose tissue (WAT) depots and the morphology of adipocytes were similar to euthyroid rats. Serum leptin and adiponectin expression in MOAT were altered by hypothyroidism. The expression of Perilipin 1, HSL, UCP1 and PRDM16 was significantly lower in MOAT of hypothyroid animals. Hypothyroidism in rats leads to a compensated EB by inducing a white adipocyte dysfunction and a decrease in BW, BMR, FI and adipokine secretions without changing the percentage of WAT depots and the morphology of the MOAT.

Physiological response of wild guanacos to capture for live shearing

Context The use of wild guanacos (Lama guanicoe) through live capture and shearing may contribute to their conservation by providing an economic alternative to rural inhabitants. However, none of the biological impacts of this activity, including the physiological ones, have been addressed. Aims The aim of this work was to characterise the acute response of guanacos to stress after capture and shearing in terms of serum cortisol levels, heart rate, and body temperature. Methods The study was performed during 2006 and 2007 in La Payunia Reserve in western Argentina. In order to determine serum cortisol concentration, 128 blood samples were obtained and the unextracted sera were analysed by radioimmunoanalyses (RIA). Sex, age category, heart rate, body temperature and total restraint time (TRT) were also registered for each animal captured. Key results Serum cortisol levels were higher in guanacos captured and sheared during 2007 than in 2006, and male cortisol levels were consistently lower than female levels. No significant differences were observed in cortisol levels of the different age categories. A positive correlation was observed between TRT and serum cortisol concentration. The analyses of cortisol levels in relation to TRT showed differences between males and females. With handling periods longer than 80 minutes, females showed a delayed stabilisation in cortisol response when compared with males. Heart rate and body temperature showed no differences between year, sex or age categories. Conclusions The present results show that the stress response to capture and shearing in wild guanacos increased significantly with handling time. We recommend avoiding capture of large numbers of animals and keeping roundup duration short to reduce TRT. Implications This work provides new information that can improve guanaco welfare during handling and shearing and may have implications for the conservation of the species.

Asynchronic steroid activity of Leydig and Sertoli cells related to spermatogenic and testosterone cycle in Phymaturus antofagastensis

The severe environments where Phymaturus lizards inhabit in the Andes highlands and in Patagonia, Argentina, impose restrictions on their reproduction, offering a framework for the development of life history strategies to overcome hard weather conditions. Among them, prolonged female cycles, asynchrony between sexes in receptivity, and sperm storage in males, were described. Asynchrony in the reproductive timing between males and females is a consequence of different energy requirements for gametogenesis, and often imply the existence of cellular mechanisms to enhance fertilization, such as the asynchronic steroid synthesis between testicular compartments, allowing gametogenesis independently of mating. In the present study ultrastructural and hormone assays were combined for the first time in liolaemids. Specifically, morphological features of steroid activity in Leydig and Sertoli cells, and serum testosterone concentrations have been studied in the lizard Phymaturus antofagastensis. Leydig and Sertoli cells presented morphological features characteristic of steroid synthesis during the spermatogenesis, and evident asynchronic steroid production between testicular compartments. Active Sertoli cells and inactive Leydig cells were observed in spring and autumn, while in mid-summer their steroid activity was synchronic in coincidence with maximal abundance of spermatozoa in epididymis. Serum testosterone concentration was at its maximum in mid-summer (126-230 ng ml(-1)), and minimum in late spring (4-24 ng ml(-1)) and early autumn (2-17 ng ml(-1)). In view of these results, P. antofagastensis males show an original approach to adjust their reproductive activity to physiological and environmental constraints at high latitudes and altitudes in the Andean highlands of Argentina.

Effect of hypothyroidism on hormone profiles in virgin, pregnant and lactating rats, and on lactation

Thyroid dysfunctions can produce reproductive problems. Untreated maternal hypothyroidism has serious consequences on development of offspring, resulting in stunted growth and mental retardation. The effects of propylthiouracyl-induced hypothyroidism (0.1 g l(-1) in drinking water starting 8 days before mating, or given to virgin rats for 30 or 50 days) on the serum profiles of hormones related to reproduction and mammary function (prolactin, growth hormone (GH), progesterone, corticosterone, oestradiol, insulin-like growth factor I (IGF-I), thyroid-stimulating hormone (TSH), triiodothyronine and tetraiodothyronine), and on mammary function in virgin, pregnant and lactating rats, were investigated. Propylthiouracyl treatment severely decreased circulating triiodothyronine and tetraiodothyronine concentrations, and increased serum TSH concentrations. Virgin rats showed prolonged periods of vaginal dioestrus, increased circulating progesterone concentrations and afternoon peaks of prolactin concentration, which are indicative of prolactin-induced pseudopregnancy. Propylthiouracyl-treated virgin rats had mammary development comparable to that of midpregnancy, and half of these rats had increased mammary casein and lactose concentrations. Serum prolactin concentrations were decreased on the afternoon of day 5 of pregnancy, increased during late pregnancy (days 15-21) and were normal during lactation. Circulating GH concentrations decreased on days 15-21 of pregnancy, whereas progesterone concentrations increased during late pregnancy and early lactation. Circulating oestradiol (measured in late pregnancy and in virgin rats), IGF-I and corticosterone concentrations were decreased. Although assessment of mammary histology showed no differences in extent of development, casein content was increased in propylthiouracyl-treated rats on day 21 of pregnancy; litter growth was severely reduced and at day 20 of age the pups were hypothyroid, with decreased GH serum concentrations. An acute suckling experiment was performed on days 10-12 of lactation to determine whether some impairment in mammary function or the suckling reflex might account for these differences. After an 8 h separation of mothers from their litters and 30 min of suckling, circulating prolactin values were not affected by propylthiouracyl treatment, but serum oxytocin concentration and milk excretion were reduced. In conclusion, hypothyroidism induces various alterations in the hormone profiles of virgin and pregnant rats, and induces pseudopregnancies and mammary development in virgin rats. These alterations do not appear to have an overt impact on the outcome of pregnancy and on mammary function during lactation, with the exception of the milk ejection reflex, which may account at least partially for the reduced litter growth.

Role of prolactin in the regulation of cytosolic NADP isocitrate dehydrogenase in the liver of the male rat

The activity of cytosolic NADP-linked isocitrate dehydrogenase (ICDH) in rat liver was determined. The administration of 2-bromo-alpha-ergocryptine (CB-154) to male rats produced a significant increase of the enzyme activity and a decrease of serum prolactin (PRL) levels in relation to control animals. Male rats 21 days after castration had lower levels of serum prolactin and higher activity of the enzyme than controls. Injection of PRL to castrated male rats lowered the enzymatic activity to control values. In intact rats injected with prolactin, the activity of the enzyme also decreased. Female rats were separated into the following groups: (a) virgins; (b) rats on day 15 of lactation; (c) ovariectomized rats. The enzymatic activity was similar in the different groups, but significantly higher than in male rats. However, serum PRL was significantly increased in 15 days lactating rats and decreased in ovariectomized ones in relation to virgins. We conclude that PRL regulates hepatic ICDH activity in male, but not in female rats. Incubation of isolated hepatocytes from intact or castrated male rats maintained the difference in ICDH activity observed in vivo, while there were no differences in ICDH activity in non-parenchymal cells. Addition of PRL, CB-154, androgens or antiandrogens to isolated hepatocytes from intact and castrated rat, had no effect on the ICDH activity, suggesting that the effect of PRL is exerted at the transcriptional level.

Hyperthyroidism and production of precocious involution in the mammary glands of lactating rats

This study investigated the influence of chronic hyperthyroidism on mammary function in lactating rats and the effects on their pups. Thyroxine-treated (10 microg per 100 g body weight per day; hyperthyroid (HT)) or vehicle-treated rats were mated 2 weeks after the start of treatment and killed with their litters on days 7, 14 and 21 of lactation. Serum concentrations of triiodothyronine (T(3)) and tetraiodothyronine (T(4)) increased in thyroxine-treated rats. In HT mothers, serum prolactin decreased on day 7 and day 14 of lactation, whereas insulin-like growth factor I (IGF-I) and progesterone concentrations decreased, and corticosterone increased on day 7 of lactation. In HT pups, T(4) concentration increased on day 7 and day 14 of lactation, whereas T(3) increased only on day 14 of lactation, and growth hormone increased on day 7 of lactation. Mammary prolactin binding sites did not vary, but there was an increase in the binding sites in the liver on day 14 of lactation in thyroxine-treated rats. In an acute suckling experiment, thyroxine-treated rats released less oxytocin, growth hormone and prolactin and excreted less milk than did control rats. Mammary casein, lactose and total lipid concentrations in thyroxine-treated rats were similar to those of control rats on day 14 of lactation. Histological studies of the mammary glands showed an increased proportion of alveoli showing reduced or no lumina and cells with condensed nuclei on day 14 and day 21 of lactation; the TdT-mediated dUTP nick-end labelling (TUNEL) test revealed an increase in apoptosis in alveolar cells on day 21 of lactation in thyroxine-treated rats. Expression of SGP-2, a gene expressed during mammary involution, increased in thyroxine-treated rats on day 14 and day 21 of lactation, whereas expression of insulin-like growth factor binding protein 5, a proapoptotic signal, was unchanged. Bcl-2, which promotes survival of mammary gland epithelial cells was unchanged, whereas expression of IGF-I, which also promotes survival of mammary gland epithelial cells, increased on day 21 of lactation in thyroxine-treated rats. These results indicate that thyroxine treatment produces some milk stasis as a result of impairments in suckling induced release of oxytocin that may initiate the first stage of mammary involution, increasing apoptosis in a gland that is otherwise actively producing and secreting milk.

Hyperthyroidism and production of precocious involution in the mammary glands of lactating rats

This study investigated the influence of chronic hyperthyroidism on mammary function in lactating rats and the effects on their pups. Thyroxine-treated (10 microg per 100 g body weight per day; hyperthyroid (HT)) or vehicle-treated rats were mated 2 weeks after the start of treatment and killed with their litters on days 7, 14 and 21 of lactation. Serum concentrations of triiodothyronine (T(3)) and tetraiodothyronine (T(4)) increased in thyroxine-treated rats. In HT mothers, serum prolactin decreased on day 7 and day 14 of lactation, whereas insulin-like growth factor I (IGF-I) and progesterone concentrations decreased, and corticosterone increased on day 7 of lactation. In HT pups, T(4) concentration increased on day 7 and day 14 of lactation, whereas T(3) increased only on day 14 of lactation, and growth hormone increased on day 7 of lactation. Mammary prolactin binding sites did not vary, but there was an increase in the binding sites in the liver on day 14 of lactation in thyroxine-treated rats. In an acute suckling experiment, thyroxine-treated rats released less oxytocin, growth hormone and prolactin and excreted less milk than did control rats. Mammary casein, lactose and total lipid concentrations in thyroxine-treated rats were similar to those of control rats on day 14 of lactation. Histological studies of the mammary glands showed an increased proportion of alveoli showing reduced or no lumina and cells with condensed nuclei on day 14 and day 21 of lactation; the TdT-mediated dUTP nick-end labelling (TUNEL) test revealed an increase in apoptosis in alveolar cells on day 21 of lactation in thyroxine-treated rats. Expression of SGP-2, a gene expressed during mammary involution, increased in thyroxine-treated rats on day 14 and day 21 of lactation, whereas expression of insulin-like growth factor binding protein 5, a proapoptotic signal, was unchanged. Bcl-2, which promotes survival of mammary gland epithelial cells was unchanged, whereas expression of IGF-I, which also promotes survival of mammary gland epithelial cells, increased on day 21 of lactation in thyroxine-treated rats. These results indicate that thyroxine treatment produces some milk stasis as a result of impairments in suckling induced release of oxytocin that may initiate the first stage of mammary involution, increasing apoptosis in a gland that is otherwise actively producing and secreting milk.

Hyperthyroidism affects lipid metabolism in lactating and suckling rats

Two per thousand pregnant women have hyperthyroidism (HT), and although the symptoms are attenuated during pregnancy, they rebound after delivery, affecting infant development. To examine the effects of hyperthyroidism on lactation, we studied lipid metabolism in maternal mammary glands and livers of hyperthyroid rats and their pups. Thyroxine (10 microg/100 g body weight/d) or vehicle-treated rats were made pregnant 2 wk after commencement of treatment and sacrificed on days 7, 14, and 21 of lactation with the litters. Circulating triiodothyronine and tetraiodothyronine concentrations in the HT mothers were increased on all days. Hepatic esterified cholesterol (EC) and free cholesterol (FC) and triglyceride (TG) concentrations were diminished on days 14 and 21. Lipid synthesis, measured by incorporation of [3H]H2O into EC, FC, and TG, fatty acid synthase, and acetyl CoA carboxylase activities increased at day 14, while incorporation into FC and EC decreased at days 7 and 21, respectively. Mammary FC and TG concentrations were diminished at day 14; incorporation of [3H]H2O into TG decreased at days 7 and 21, and incorporation of [3H]H2O into FC increased at day 14. In the HT pups, growth rate was diminished, tetraiodothyronine concentration rose at days 7 and 14 of lactation, and triiodothyronine increased only at day 14. Liver TG concentrations increased at day 7 and fell at day 14, while FC increased at day 14 and only acetyl CoA carboxylase activity fell at day 14. Thus, hyperthyroidism changed maternal liver and mammary lipid metabolism, with decreased lipid concentration in spite of increased liver rate of synthesis and decreases in mammary synthesis. These changes, along with the mild hyperthyroidism of the litters, may have contributed to their reduced growth rate.

Receptors and neurotransmitters involved in the dual modulation of prolactin release by the serotoninergic system in pregnant and lactating rats

The receptors and neurotransmitter pathways that may participate in the inhibitory action of 5-hydroxytryptamine (5HT) on prolactin release during late pregnancy and lactation in rats were studied. Administration of the 5HT synthesis inhibitor, p-chlorophenylalanine, to late pregnant rats induced a significant increase in serum prolactin concentrations at 17:00 h on day 19 of pregnancy that was partially blocked by injections of the 5HT precursor, 5-hydroxytryptophan, or the 5HT agonists, 8-hydroxy-2-(di-n-propylamino)-tetralin hydrobromide (S1a), 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (S2) and N-(3-chlorophenyl)imidodicarbonimide diamide HCl (S3), but not by RU 24969 (S1b) or 1-meta-(chlorophenyl)-piperazine-2-HCl (S1a-2c). The 5HT neurotoxins, fenfluramine and p-chloroamphetamine, which selectively destroy fine axon serotoninergic fibres but not coarse ones, prevented the increase in circulating prolactin observed at 18:00 h on pro-oestrus and on day 21 of pregnancy, but did not modify serum prolactin concentrations at 17:00 h on day 19 of pregnancy. Administration of the adrenergic antagonists, metoprolol or prazosin, also prevented the stimulatory effects of p-chlorophenylalanine or ketanserin in pregnant rats on day 19 (17:00 h) or on days 10-12 (16:30 h) in lactating rats separated from their litters. Administration of p-chlorophenylalanine to pregnant rats on day 19 reduced dopamine concentrations in the arcuate nucleus and in the anterior hypothalamus and noradrenaline concentrations in the anterior hypothalamus and the suprachiasmatic nucleus. These results indicate that the inhibitory actions of 5HT on prolactin release in pregnant and lactating rats are mediated by S1a, S2a and S3 receptors and by the coarse axon serotoninergic fibres. In addition, the inhibitory actions of 5HT may modulate the action of a stimulatory adrenergic pathway, as well as the concentrations of noradrenaline and dopamine in different hypothalamic areas, which, in turn, particularly arcuate nucleus dopamine, regulate prolactin release.

Effect of chronic thyroxine treatment on pregnancy in rats: effects on oestrogen, progesterone, prolactin and GH receptors in uterus, liver and mammary gland

We have previously shown that experimental hyperthyroidism produces premature and difficult delivery and absence of lactation in spite of apparently adequate luteolysis and lactogenesis. To study the possible causes of these alterations we measured the effect of treatment with T4 (0.25 or 1 mg kg(-1), s.c., daily, started 10-15 days before mating, HT0.25 and HT1) on serum hormones and their receptor (R) concentrations in reproductive tissues on day 20 of pregnancy (1800 hours), comparing them with controls on the same day (C20), or on day 21 of pregnancy (1800 hours) (C21). Serum prolactin (PRL) and corticosterone (B) concentrations increased in the HT groups, progesterone (Pg) and GH decreased and estradiol (E2) did not change, compared with C20 group. C21 rats had increased serum PRL and decreased Pg and GH. In HT rats mammary DNA and protein tissue content was doubled. Receptor concentrations were expressed per mg DNA. Mammary PRL-R were increased in HT1 rats, while E-R and Pg-R were significantly lower in both HT groups. HT0.25 and HT1 rats had increased uterine E-R and Pg-R and decreased liver PRL-R and GH-R as well as their mRNAs. Liver E-R, PRL-R and GH-R were decreased in C21 rats, while uterine Pg-R were increased. Thus, some of the observed changes (serum Pg and GH, mammary and uterine Pg-R, and liver GH-R and PRL-R decreases and serum PRL increase) may be due at least partially to the advancement in luteolysis and delivery, being similar to the changes observed between days 20 and 21. The changes in serum B, mammary PRL-R, and mammary and uterine E-R may be caused solely by the T4 treatments and may play a role in the alterations previously observed.

In vivo study of prolactin (PRL) intracellular signalling during lactogenesis in the rat: JAK/STAT pathway is activated by PRL in the mammary gland but not in the liver

The rat prolactin receptor (PRL-R) exists in two forms, which differ in the length of the cytoplasmic domains, tissue distribution, and biological activity. The short form predominates in liver while the long form is prevalent in mammary gland. We have compared activation by PRL of the JAK2-STAT pathway (protein tyrosine phosphorylation and STAT5 activation) in mammary gland and liver in an in vivo rat model of induction of lactogenesis by PRL injections, and we have studied the relative proportion of both forms of the receptor in these tissues by reverse transcription-polymerase chain reaction. Rats were ovario-hysterectomized on Day 19 of pregnancy, treated with bromocriptine, subsequently injected with 250 micrograms ovine PRL i.p. on Day 20, and killed 0-12 h after. Western blots of solubilized mammary gland and liver membranes immunoprecipitated with anti-PRL-R or anti-JAK2 antibodies showed that the PRL-R is constitutively associated with JAK2 and that the long form of the PRL-R is present in both tissues, while the short form was detected only in liver. Phosphorylated proteins corresponding to the long form of PRL-R and JAK2 appeared 15-60 min after ovine PRL injection in mammary extracts but not in liver. At these same times, an electrophoretic mobility shift assay, using a rat beta-casein probe specific for STAT5 binding, showed activated STAT5 in mammary gland cytosol and nuclear extracts. In the liver, low levels of activated STAT5 were detected in non-treated animals, which were not modified by PRL. Quantitative RT-PCR of liver and mammary PRL-R mRNA showed that the amount of the long form of PRL-R mRNA is roughly comparable in both tissues, while the short form is predominant in liver and in a minority in mammary tissue. Both forms were down-regulated by PRL only in mammary glands. Thus, during lactogenesis, mammary tissue responds to PRL by activation of JAK2 and STAT5, while the liver does not respond to PRL in spite of the presence of PRL-R associated with JAK2 and pre-existing activated STAT5. Thus, liver tissue may lack a critical component for activation of the PRL pathway, or the large quantities of the short form of the PRL-R may associate with the long form to constitute inactive heterodimers.

Effect of chronic thyroid hormone treatment on cycling, ovulation, serum reproductive hormones and ovarian LH and prolactin receptors in rats

We studied the effect on cycling, ovulation and hormone secretion of a chronic thyroxine treatment (HT, 1 mg/kg,S.C., daily, initiated at oestrus) on female rats. HT rats showed normal 4-day vaginal cycles on the first three cycles after initiation of the treatment, but on the fourth cycle had a prolonged oestrus and subsequently entered in constant di-oestrus. In spite of the normal vaginal cycles only 66%, 50%, 33% and 10% of the HT rats ovulated on cycles 1 to 4 respectively. In contrast, during cycles 2 and 3, ovulating HT rats shed a significantly greater number of ova than controls. Hormones were measured at 12.00 and 18.00 h (pre-ovulatory) on prooestrus and at 11.00 h on oestrus. HT ovulating rats had normal LH levels on the first two cycles, but low levels on the third one, while non-ovulating HT rats had low preovulatory LH levels. Serum FSH concentrations were elevated in all the HT rats on cycles 1 and 2 and on pro-oestrus morning in cycle 3 and may have been responsible for the increase in ovulation rate. On oestrus, ovulating HT rats had higher FSH values than nonovulating ones. Serum prolactin levels were similar to controls in all the HT rats on cycle 1, but on the subsequent cycles pre-ovulatory levels were lower than controls in all the HT rats, while values were increased in the non-ovulating HT rats on the third and fourth oestrus mornings. Pro-oestrous serum oestradiol concentrations in all the HT rats were not different from controls on cycles 1 and 2 and diminished on 3 and 4. Oestrous levels were significantly lower on the cycle 1 and only on the nonovulating HT rats on cycle 2. Serum progesterone levels had values similar to those of FSH, with increased values in the first two cycles. Serum corticosterone levels were increased in the mornings of cycles 2 and 3, but values were normal on the fourth one. Ovarian prolactin and LH receptor mRNAs, measured on HT rats on the third prooestrus by Northern blotting, showed significant increases in all the majoritary molecular forms (2.5 and 7 kb for LH receptor and 0.9, 2.9-3, 5 and 10 kb for the prolactin receptor) with respect to control pro-oestrous rats. These results show a progressive disruption of cycling, ovulation and hormonal secretion after the initiation of a chronic thyroid hormone treatment in rats, which eventually lead to an anovulatory state. These results may be of importance for the interpretation of the reproductive disfunctions provoked by hyperthyroidism in women.

Lactogenic actions of different growth hormone preparations in pregnant and lactating rats

We studied the capacity of different GH preparations, natural human (h)GH, recombinant hGH (rhGH), rat (r)GH, ovine (o)GH, bovine (b)GH and porcine (p)GH, and ovine prolactin (oPRL), to stimulate lactogenesis in ovario-hysterectomized pregnant rats or intact lactating rats treated with bromocriptine (BC). Ovariohysterectomy (OVX-HYS) performed at 0800 h on day 19 of pregnancy induced lactogenesis, i.e. increases in mammary casein and lactose and positive response to the oxytocin test, 28 h later. Lactogenesis was prevented by treatment with BC (1.5 mg/kg) immediately after surgery (OVX-HYS-BC). The hormones were given at doses of 0.25 or 0.5 mg/rat (except rhGH given only at 0.5 mg/rat) at 1200 and 2000 h on day 19. Casein was increased by both doses of oPRL and hGH, rhGH and 0.25 mg oGH, and lactose by both doses of oPRL, rhGH and 0.25 mg rGH. The other GH preparations had no effect. The oxytocin test demonstrated the presence of milk in the mammary tissues of the OVX-HYS rats and in the OVX-HYS-BC plus oPRL (0.25 and 0.5 mg) or rhGH-treated groups. Injection of BC to pregnant rats at 2000 h on day 20 and at 0800 h on day 21 decreased litter growth on the first 4 days postpartum. Two-thirds of the litters resumed growth after day 4, indicating the recuperation of milk production, while the rest never recuperated. Serum prolactin in BC-treated rats was reduced until day 4 postpartum. On day 6 the rats which had recuperated had normal values, while those which had still not recuperated had lower values. BC-treated rats were injected s.c. with 0.25 mg each of oPRL, hGH, rGH, oGH, bGH or pGH, or 0.25 or 0.5 mg rhGH/rat, immediately postpartum and 12, 24 and 36 h later. hGH and 0.5 mg rhGH induced levels of milk production similar to controls except on day 3. oPRL and rhGH (0.25 mg), induced a partial reversion of the effect of BC. rGH and oGH had a slight effect on days 1 and 2 and all the litters resumed growth on day 7. In contrast, pGH and bGH were inactive. The affinity of hGH for the prolactin receptor, measured as displacement of 125I-labelled oPRL binding to crude liver membranes, was comparable with that of oPRL. While rhGH was ten times less active than oPRL, rPRL was 100 times lower and all the other GH preparations had at least 10(4) times lower capacity to displace 125I-labelled oPRL.(ABSTRACT TRUNCATED AT 400 WORDS)

Correlation of growth hormone secretion during pregnancy with circulating prolactin in rats

Growth hormone (GH) concentrations were measured throughout pregnancy in rats. The effects of surgical stress, ovariectomy, and treatments with the antiprogesterone mifepristone (RU 486) or the antioestrogen tamoxifen on serum GH, progesterone and prolactin were studied. GH concentrations were low during the first 18 days of pregnancy, except on the morning of day 5, and increased progressively from day 19 reaching peak values on the mornings of days 21 and 22. Thereafter GH concentrations decreased progressively, reaching very low values at 24.00 h on day 22, in parallel with a rise in serum prolactin concentrations. Surgical stress, performed at 12.00 h on day 20 of pregnancy, diminished serum GH concentrations 10 min later, but these returned to values similar to those of the non-operated rats 1-24 h later. Surgical stress did not modify serum prolactin concentrations at any time. Ovariectomy performed on the morning of day 19 produced the expected fall in serum progesterone and a rise in prolactin which lasted until the night of day 20. Serum GH concentrations were significantly diminished with respect to controls on day 20 and the morning of day 21 and then increased. Treatment with mifepristone on day 19 produced a simultaneous rise in serum prolactin and a fall in serum progesterone and GH by 08.00 h on day 21. Treatment with tamoxifen on days 3 and 4, or given daily from day 17 onwards did not modify prolactin concentrations but diminished serum GH concentrations at 08.00 on day 5 and on days 19-22, with the exception of a peak on day 22 (08.00 h). Tamoxifen also decreased serum progesterone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic thyroid hormone administration on pregnancy, lactogenesis and lactation in the rat

We studied the effects of daily administration of 1 mg/kg thyroxine (T4) starting 10-15 days before mating, on parturition, maternal behavior and lactation in rats. Treated rats had elevated serum titers of T3 and T4, a greater number of fetuses and parturition was advanced approximately 12 h and lasted longer than in controls. None of the treated rats were able to lactate because of defects in maternal behavior and milk ejection; the litters died usually within 48 h postpartum. In rats sacrificed at 10.00 on day 21 of pregnancy, mammary gland content of total protein, phospholipids, casein and lactose were significantly increased, but total lipid was markedly reduced. Lipogenesis was also significantly increased, as well as the activity of the lipogenic enzymes glucose-6-phosphate dehydrogenase, fatty acid synthetase and isocitrate dehydrogenase. These results are indicative of normal albeit premature lactogenesis. The T4-treated rats also had advances in the prepartum fall in serum progesterone and the increase in prolactin as well as in the increase in mammary casein and lactose concentrations of approximately 12 h with respect to control pregnant rats. These results show that chronic T4 treatment induces an advance of approximately 12 h in luteolysis, which in turn advances lactogenesis and parturition in rats. Although the mammary gland was able to produce milk, lactation failed due to abnormal maternal behavior and milk ejection, the causes of which are still unknown. Other effects of hyperthyroidism were also present, such as a severe reduction in lipid content of the gland.(ABSTRACT TRUNCATED AT 250 WORDS)

Amelioration of some metabolic effects produced by hyperthyroidism in late pregnant rats and their fetuses. Effects on lipids and proteins

We have studied the effect of 40-45 days administration of 1 mg/kg thyroxine on protein and lipid metabolism in liver, heart, lungs, kidneys and adrenal glands of virgin and 21-day pregnant rats and their fetuses and placentae. The chronic administration of thyroid hormone produced significant increases in serum T3 and T4 in both groups as well as in organ weights and protein concentrations in virgin rats, but much smaller modifications in pregnant ones. Hyperthyroidism decreased the weight of fetal livers and increased that of placentae; protein content was increased in all fetal organs. Hyperthyroidism induced increases in phospholipid concentrations in all the organs and in total lipids only in liver and heart of adult rats, which were not counteracted by pregnancy. Pregnant rats had increases in total lipids in liver and kidneys and in adrenal phospholipids. In hyperthyroid fetuses there was an increase in hepatic total lipids and no changes in phospholipids. Hepatic lipogenesis (measured by in vivo incorporation of 3H2O into lipids) was increased by hyperthyroidism in virgin and pregnant rats, but the increase was significantly smaller in the pregnant hyperthyroid rats compared with the virgin ones. Fetal lipogenesis in liver and lung was not changed. In addition, an increase was observed in lipogenic enzyme (fatty acid synthetase and glucose-6-phosphate dehydrogenase) activities in hyperthyroid virgin rats which was prevented by pregnancy. In fetuses only pulmonary glucose-6-phosphate dehydrogenase was increased when expressed in terms of tissue weight. Our results indicate that the metabolic effect of hyperthyroidism is attenuated in pregnant rats and their fetuses, when compared with adult virgin rats, in most of the parameters studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of the adrenergic system on the release of prolactin and lactogenesis at the end of pregnancy in the rat

The part played by the adrenergic system on the release of prolactin and lactogenesis induced by prostaglandin F2 alpha and the antiprogesterone RU 486 was studied in pregnant rats. Two doses of prostaglandin F2 alpha (150 micrograms) administered at 08.00 and 12.00 h on day 19 of pregnancy induced, at 12.00 h on day 20 (24 h after administration), a significant increase in the serum concentration of prolactin, with a significant decrease in serum progesterone levels. These hormonal changes significantly augmented casein and lactose levels in the mammary gland. Treatment with RU 486 (2 mg/kg) at 08.00 h on day 19 augmented casein and lactose concentrations in the mammary gland at 12.00 h on day 20 without modifying serum concentrations of prolactin and progesterone. The adrenergic antagonists, propranolol (3 mg/kg), metoprolol (10 mg/kg), ICI 118,551 (200 micrograms/kg), idazoxan (100 micrograms/kg) and prazosin (10 mg/kg), were administered s.c. at 12.00 and 20.00 h on day 19 and 08.00 h on day 20 of pregnancy to intact rats or to rats previously treated with RU 486 or prostaglandin F2 alpha. These adrenergic antagonists did not modify serum prolactin or progesterone levels in intact or RU 486-treated rats, but serum prolactin levels in the prostaglandin F2 alpha-treated group were significantly reduced by treatment with propranolol, metoprolol or prazosin. In addition, propranolol and ICI 118,551 also decreased the casein and lactose concentrations in the mammary glands of RU 486- and prostaglandin F2 alpha-treated rats, while the other compounds had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin receptor gene expression in rat mammary gland and liver during pregnancy and lactation

The expression of two forms of PRL receptor messenger RNA was measured at different stages of pregnancy and lactation in mammary gland and liver from Sprague-Dawley rats, using 32P-labeled complementary DNA probes encoding the extracellular part of the receptor (E probe), common to the two forms and a probe encoding the intracellular part of the long form of the receptor (I probe), that only recognizes sequences specific to the long form of the receptor. Hybridizations were performed in Northern blots obtained from electrophoreses of poly (A+) enriched RNA preparations from mammary glands and livers of rats on days 0, 6, 12, 19, and 21 of pregnancy and 5, 10, 15, and 20 of lactation. The Northern blots were also hybridized with a chicken beta-actin probe, to correct for the amount of mRNA added and the different metabolic states of the tissues. Both tissues expressed the same forms of PRL receptor mRNAs, namely bands at 2.5, 3, and 5.5 kilobases encoding the long form of the receptor and a major band at 1.8 kilobases encoding the short form. The liver expressed all the receptor mRNA forms in much higher quantity than the mammary gland, independent of the reproductive state. In liver there was an increase of all the transcripts on day 19 of pregnancy, followed by an abrupt decline at the onset of lactation, to levels lower than those of virgin rats. In contrast, mammary gland PRL receptor mRNAs were low in virgin and pregnant animals, increased significantly at day 21 of pregnancy, and continued to increase throughout lactation. Treatment of day 19 pregnant rats with the antiprogesterone RU 486 induced, 24 h later, PRL receptor mRNAs in mammary gland but not in liver. There were no significant differences in the relative proportions of long to short forms of PRL receptor mRNAs at the different reproductive states, but the proportion of the long form was slightly greater in mammary gland than in liver. Membrane PRL receptor concentrations were also measured in the same tissues used for the mRNA study by binding to a 125I-labeled monoclonal antibody (U5), which specifically recognizes the PRL receptor at a site different from the hormone binding site. The quantity of receptor measured by U5 binding was approximately 3 times higher than that measured with 125I-labeled ovine PRL.(ABSTRACT TRUNCATED AT 400 WORDS)

Simultaneous determination of trimipramine and its major metabolites by high-performance liquid chromatography

Trimipramine is a tricyclic antidepressant drug often assayed by gas chromatographic or gas chromatographic-mass spectrometry techniques. A high-performance liquid chromatographic method with electrochemical detection is described for the assay of trimipramine and its major metabolites, monodesmethyltrimipramine and 2-hydroxytrimipramine, in plasma. The method is sensitive, accurate and robust and thus suitable for routinely assaying samples following single doses of trimipramine to man. The assay was applied to plasma samples obtained following a single 50-mg dose of trimipramine to healthy volunteers.

Effect of DMBA on the expression of prolactin receptors and IGF1 genes in rat mammary gland

Prolactin receptor and IGF1 gene expression were measured in mammary glands from Sprague-Dawley rats at different times (10, 30; and 58 d) after administration of a single dose of 15 mg dimethylbenz(a)-anthracene (DMBA) per os at 55 d of age, and in DMBA-induced mammary tumors appearing in these rats at approximately 2 months after DMBA administration; The relative gene expression of prolactin receptor and insulin-like growth factor (IGF1) mRNAs was measured by hybridization to Northern blots prepared from pools of tissue. The probes used were 32P-labelled cDNAs specific to the extracellular domain of the receptor (E probe), common to all forms, and a probe specific to the intracellular position of the long form of the receptor (I probe), a human IGF1 probe, and chicken beta-actin probe, to correct for loss of tissue and different metabolic activity of the tissues. Hybridization with the prolactin receptor probes revealed bands at 2.5, 3; and 5.5 kb hybridizing with the long form of the receptor and a more intense band at 1.8 kb that corresponded to the short form of the receptor. There were no changes in the relative expression of prolactin receptor mRNAs in the mammary gland of control (oil-treated) or DMBA-treated rats, although there was a gradual diminution of expression with increasing age of the animals. In contrast, in DMBA-induced mammary tumors, there was a marked increase in the relative expression of prolactin receptor mRNAs with, however, no modification in the relative proportion of short and long forms.(ABSTRACT TRUNCATED AT 250 WORDS)

Suckling-induced prolactin release potentiates mifepristone-induced lactogenesis in pregnant rats

Suckling, starting at 19:00 h on Day 18 of pregnancy, induced a significant increase in serum prolactin concentration at 20:00 h on Day 19 of pregnancy, but no increase in mammary gland casein or lactose content. Mifepristone (2 mg/kg) injection at 08:00 h on Day 19 of pregnancy induced significant increases in casein, but not in lactose, 24 h after administration. Mifepristone alone did not induce prolactin secretion, indicating that lactogenesis was induced by placental lactogen in the absence of progesterone action. When mifepristone was injected into suckling rats, serum prolactin concentrations were higher than in the untreated suckling rats. Casein in these rats increased significantly 12 h after mifepristone administration and lactose at 24 h after. If the suckling mifepristone-treated rats were given two injections of bromocriptine (1.5 mg/kg) at 12:00 h on Days 18 and 19 of pregnancy, serum prolactin concentrations were not increased by suckling, but casein and lactose concentrations in the mammary gland showed values similar to those obtained in the mifepristone-treated non-suckling rats. Mifepristone can therefore potentiate suckling-induced prolactin release in pregnant rats, demonstrating a direct central inhibitory action of progesterone on prolactin secretion. This suckling-induced prolactin secretion, unable to induce casein or lactose synthesis in the presence of progesterone, enhanced significantly synthesis of these milk components in the absence of progesterone action (rats treated with mifepristone). Fatty acid synthase, which is stimulated by the suckling stimulus in lactating rats, was not modified by mifepristone or suckling in pregnant rats.

Inhibition of casein synthesis by progestagens in vitro: modulation in relation to concentration of hormones that synergize with prolactin

We studied the effect of progesterone and its agonist, R 5020, on casein and transferrin production in pregnant rabbit mammary gland explant culture and its modulation by hormones that synergize with prolactin. The glands were obtained from rabbits on days 12-14 of gestation. The progestins had no effect alone, but significantly inhibited ovine and porcine prolactin stimulation of casein synthesis in a dose dependent manner. There were no effects on transferrin content of the tissue, demonstrating a specific effect of progesterone on casein synthesis. In approx 15% of the cultures, prolactin stimulated casein production to very high levels and the progestins lost their inhibitory action. Progestins were also ineffective when the tissue was cultured with prolactin and unphysiologically high levels of insulin (5 mg/l) or cortisol (280 nmol/l), which stimulated casein synthesis to higher levels than prolactin alone. The concentration of cortisol used was 10 times higher than the serum levels seen in rabbits at the stage of gestation studied (approx 10 ng/ml) and corresponded to levels seen at the end of gestation, a period when the glands are secreting milk and progesterone serum levels have commenced to decrease. Thus, when the prolactin effect upon casein synthesis had been potentiated, whether spontaneously or through synergism with insulin or corticoids, progestins were unable to inhibit it, as is the case in lactating tissues. The results show that utilization of unphysiological levels of hormones in culture may distort the response of the tissue, masking responses that are clearly seen in vivo.

Feedback regulation by progesterone of stress-induced prolactin release in rats

We have previously found that modifications to serum progesterone concentration have profound inhibitory effects on prolactin release in response to ether stress. The objective of the present study was to determine the effect of ether stress on progesterone secretion and the role of this steroid in ether-induced prolactin release. Serum progesterone concentration, 5 min after ether stress had been applied over a 2-min period, was consistently increased in male rats, in cyclic rats on the mornings of pro-oestrus and oestrus, and in androgenized rats in permanent oestrus. Ovariectomized androgenized rats showed the same response. Adrenalectomy of male and female rats abolished the progesterone increase induced by stress. Thus, the progesterone secreted by stressed rats is mostly of adrenal origin. In groups of male and pro-oestrous rats, circulating concentrations of prolactin and progesterone were measured from 5 to 60 min after stress. In both sexes the serum prolactin concentration was significantly increased at only 5 and 10 min after stress when compared with control values. In pro-oestrous rats the serum progesterone concentration was significantly higher than in controls at 5, 10 and 20 min after stress, whilst in male rats the concentration remained significantly higher at 30 min. Thirty minutes after the first stress, male and proestrous rats were etherized for 2 min, and bled 5 min after removal from the ether container. In female rats this second stress produced only a slight but significant increase in serum prolactin concentrations, whereas in male rats prolactin concentrations did not increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of serotonin antagonists on prolactin and progesterone secretion in rats: evidence that the stimulatory and inhibitory actions of serotonin on prolactin release may be mediated through different receptors

The serotoninergic regulation of prolactin release was studied in female rats in different reproductive states using ketanserin, a specific S2 receptor blocker, ICS 205-930 ((3 alpha-tropanyl)1H-indol-3-carboxylic acid ester), a specific S3 receptor blocker and p-chlorophenylalanine (pCPA), a serotonin synthesis inhibitor. Administration of ketanserin to pro-oestrous rats inhibited the afternoon prolactin surge; this inhibition was prevented by progesterone. On day 3 of pregnancy, pCPA or ketanserin blocked the afternoon prolactin surge, and administration of oestrogen (on day 2) and progesterone (on day 3) in combination, but not alone, prevented this effect. On day 9 of pregnancy, treatment with oestrogen (on day 8) and progesterone (on day 9) induced an afternoon surge of prolactin which was prevented by administration of ketanserin or pCPA. On days 9 and 16, pCPA induced a slight increase in serum prolactin in rats not treated with steroids, but ketanserin had no effect. On day 13, ketanserin and pCPA had no effect on serum prolactin levels, but after increasing serotoninergic transmission by injecting fluoxetine and 5-hydroxytryptophan, serum prolactin levels were decreased. On day 19, ketanserin produced a transient increase in the serum concentration of prolactin, probably produced by the marked decrease in the serum concentration of progesterone induced by the S2 receptor blocker. Administration of ICS 205-930 to pro-oestrous rats or rats on day 19 of pregnancy had no effect on serum concentrations of prolactin and progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiprogesterone and antiglucocorticoid actions of RU 486 on rabbit mammary gland explant cultures. Evidence for a persistent inhibitory action of residual progesterone upon the mammary tissue

The antiprogesterone and antiglucocorticoid compound RU 486 added to pregnant rabbit mammary gland explant cultures had no effect alone but significantly stimulated casein production in the presence of ovine prolactin (PRL) in a dose dependent manner. This stimulation was inhibited by progesterone (Pg) and the Pg agonist R5020. When the explants were cultured for 5 days with two changes of medium, to eliminate all steroids, and hormones added afterwards, the effect of PRL was potentiated, Pg was no longer inhibitory and RU 486 had no effect, RU 486 also could inhibit the stimulatory action of glucocorticoids added to the cultures along with PRL. The compound was able to displace [3H]dexamethasone and [3H]R 5020 from mammary gland glucocorticoid and Pg receptors respectively and proved to have a high relative binding affinity (RBA) for both receptors when compared with typical ligands for each receptor. The RBAs of RU 486 and the steroids used in this study to mammary gland glucocorticoid and Pg receptors correlated well with the ability of RU 486 to block their biological activities. These results demonstrate that RU 486 has both antiglucocorticoid and antiprogesterone activities in pregnant rabbit mammary glands as well as the existence of a strong inhibitory residual action of Pg in the gland that persists during the first 48 h of culture and that can be eliminated by RU 486 or after several days of culture with no hormones.

Binding and action of glucocorticoids and mineralocorticoids in rabbit mammary gland. Exclusive participation of glucocorticoid type II receptors for stimulation of casein synthesis

In order to ascertain whether the effect of corticoids upon casein synthesis in pregnant rabbit mammary gland culture is due to interactions with classical glucocorticoid or type I (mineralocorticoid) receptors we have demonstrated the existence of both types of receptors in the tissue and have studied the effects of aldosterone and the specific glucocorticoid agonist RU 28362 upon casein synthesis in tissue culture. Both compounds significantly stimulated prolactin-induced casein synthesis. On dose-response studies RU 28362 proved to be as active as dexamethasone, cortisol was active at intermediate concentrations and aldosterone was the least active. The three glucocorticoids were able to stimulate DNA synthesis in the tissue, but aldosterone had no effect. Finally, RU 486, a potent glucocorticoid antagonist, blocked the action of aldosterone and the other corticoids upon casein synthesis, whereas spironolactone, a mineralocorticoid antagonist, was unable to do so. These results demonstrate that the stimulatory effect of corticoids upon casein synthesis in pregnant rabbit mammary tissue culture is mediated through classical (type II) glucocorticoid receptors. Transferrin accumulation in the tissue was not modified by any treatment, indicating that the action of the steroids was specific for casein, and not a general stimulation of protein synthesis.

A possible dual regulation of prolactin release by the serotoninergic system in rats at pro-oestrus and during late pregnancy: role of ovarian hormones

The effect of para-chlorophenylalanine (pCPA), an inhibitor of serotonin synthesis, on prolactin release was studied in rats on the day of pro-oestrus and at the end of pregnancy (day 19). The surges of prolactin normally seen in the afternoon of pro-oestrus in intact rats and in rats ovariectomized on dioestrous day 2 and primed with oestrogen were significantly inhibited by pCPA treatment. Administration of 5-hydroxytryptophan reversed the inhibitory action of pCPA on prolactin release. Treatment with progesterone also completely reversed the inhibitory effect of pCPA on prolactin release in pro-oestrous rats and partially reversed it in ovariectomized oestrogen-treated rats. Ovariectomy on day 19 of pregnancy induced a significant release of prolactin 12 and 24 h later. Administration of pCPA on day 18 of pregnancy produced a marked increase in serum concentrations of prolactin on days 19 and 20 in rats left intact or ovariectomized on day 19. Administration of 5-hydroxytryptophan significantly reversed this stimulatory effect of pCPA on prolactin release but did not modify the release of prolactin induced by ovariectomy. Methiothepin (1-[10,11-dihydro-8-(methylthio) less than b,f greater than thiepin-10,41]-4-methylpiperazine maleate), a serotonin receptor blocker, also induced a significant increase in serum concentrations of prolactin on day 20 of pregnancy in rats left intact or ovariectomized on day 19. These results suggest the existence of different serotoninergic actions in the regulation of prolactin release at pro-oestrus and in late pregnancy. Serotonin facilitates the surges of serum prolactin released at pro-oestrus and in ovariectomized rats treated with oestrogen; progesterone enhances this effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Stress-induced prolactin release in female, male and androgenized rats: influence of progesterone treatment

Ether stress applied at 10.00 h induced a 100% increase in serum prolactin in intact and ovariectomized androgenized rats. Ovariectomy significantly diminished the basal serum prolactin values observed in intact androgenized rats. Two doses of progesterone (5 mg) given to intact and ovariectomized androgenized rats 14 and 2 h before exposure to ether stress increased prolactin values in the control groups but completely prevented the effect of stress. Exposure to ether stress induced a 100% increase in serum prolactin values in androgenized rats with increased serum progesterone levels 4 days after the induction of ovulation and the luteal phase with human chorionic gonadotropin (hCG). A group of androgenized rats with induced maternal behaviour and which had been suckled for 6 days was given 100 i.u. hCG and suckled for another 6 days after the hCG-induced luteal phase had been established. The serum prolactin and progesterone values of these rats were significantly higher than those treated with hCG only and ether stress did not increase prolactin release. A greatly increased serum concentration of prolactin was obtained in pro-oestrous and oestrous virgin rats after exposure to ether stress. Serum prolactin was also increased by stress in male rats. Progesterone administration to these female and male rats prevented stress-induced prolactin release. To ascertain the part played by dopamine and serotonin in the effect of stress on prolactin release, groups of androgenized and oestrous female rats were treated with bromocriptine or p-chlorophenylalanine methylester hydrochloride (pCPA).(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian and feto-placental factors and the regulation of prolactin release during pregnancy in the rat

Administration of progesterone (5 or 10 mg) to pregnant rats increased serum prolactin significantly on the afternoon of Days 4, 6, 7 and 8 of pregnancy, but had no effect on later days. On Day 10 progesterone administration increased serum prolactin only in rats treated with oestrogen the day before. A similar treatment with oestrogen and progesterone was unable to stimulate secretion on the afternoon of Day 13 of pregnancy. In rats from which the corpora lutea had been unilaterally removed and hence endogenous progesterone levels were 50% of the normal values, or in those that carried 4 conceptuses, progesterone treatment after oestradiol priming was partly effective in inducing prolactin release on Day 13. However, in rats ovariectomized, with bilateral excision of the corpora lutea, or with 2 conceptuses left, treatment with ovarian steroids markedly increased serum prolactin values. By Day 13 all the rats from the ovariectomized group or with bilateral excision of the corpora lutea had aborted. On Day 13, therefore, the high serum concentrations of feto-placental factors and of progesterone are responsible for the blockade of the spontaneous and ovarian steroid-induced prolactin release. On the other hand, on Day 16 of pregnancy the decrease of circulating progesterone by excision of the corpora lutea or by ovariectomy followed by oestradiol treatment significantly increased serum prolactin on Day 17. Removal of all the conceptuses did not modify the effects of these treatments. The present results demonstrate different roles of progesterone upon the control of prolactin secretion. After a stimulatory action during the first days of pregnancy, there is a change to an inhibitory control at the end of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of pituitary DNA synthesis during different reproductive states in the female rat: role of estrogens and prolactin

We studied DNA synthesis in the rat adenohypophysis during the estrous cycle, pregnancy and lactation. During the estrous cycle, DNA synthesis was 3 times higher on the morning of estrus than on the other days. This peak was abolished completely by ovariectomy or pentobarbital, which also blocked the preovulatory surges of LH and prolactin. Methallibure , which blocked the LH but not the prolaction surge, had a partial effect on DNA synthesis. An acute and significant decrease in pituitary DNA synthesis occurred between days 0 (estrus) and 1 of pregnancy, followed by a less pronounced diminution until parturition. After delivery, DNA synthesis increased steeply on day 1 of lactation, returning to low values by day 3, under normal suckling conditions. Thelectomy , which blocked suckling-induced prolactin release, or antiestrogen treatment, which did not decrease prolactin secretion, diminished pituitary DNA synthesis on day 1 of lactation. Estrogen administration to intact or ovariectomized rats on days 9-11 of lactation stimulated (100%) DNA synthesis. Ovariectomy had no effect. In conclusion, in the different reproductive states studied, pituitary DNA synthesis is related to prolactin release in the presence of estrogens.

Relationships among release of prolactin, synthesis of DNA and growth of the anterior pituitary gland of the rat: effects of oestrogen and sulpiride

The effect of daily injections of sulpiride was compared with that of a single injection of the drug in male rats which had been treated with oestradiol diundecenoate for various periods of time. We studied the effect of the different treatments on weight of the pituitary gland, concentration of prolactin and incorporation of [3H]thymidine into DNA in the pituitary gland and on serum levels of prolactin. Administration of the oestrogen produced a marked increase in the synthesis of DNA at day 7. The stimulation diminished at day 21 and was not significant at day 45. The maximum increase in the concentration of prolactin in serum and pituitary glands was observed during the first 7 days (approximately 400 and 150% respectively) and in the weight of the anterior pituitary gland after 21 days of treatment (approximately 107%).

A single injection of sulpiride markedly stimulated the release of prolactin and the synthesis of DNA at day 7. Both these effects diminished at day 21 and disappeared by day 45. Daily injections of sulpiride also produced similar changes in the release of prolactin and in the replication of DNA. The growth of the anterior pituitary gland was greater in this group than in the rats which had been treated with oestradiol diundecenoate only. After the end of treatment with oestrogen and sulpiride the pituitary weight and the concentration of prolactin in the anterior pituitary gland diminished together with levels of prolactin and oestrogen in serum. There was a good correlation between weight of the gland and serum levels of prolactin. The results further support the idea of a mechanism which controls the proliferation of lactotrophs in which the release of the hormone is accompanied by an increase in pituitary DNA synthesis.

Effect of haloperidol on the synthesis of DNA in the pituitary gland of the rat

The administration of haloperidol increased serum prolactin and decreased the pituitary concentration of prolactin 15 min after its administration. Concomitantly there was a stimulation in the synthesis of DNA and the activity of DNA polymerase alpha in the anterior pituitary gland that was greater in oestrogenized than in non-oestrogenized male rats. Both these effects were greatly reduced by clomiphene in the oestrogenized male rats, although it did not affect the release of prolactin produced by haloperidol. In non-oestrogenized animals clomiphene abolished the stimulatory effect of haloperidol on the synthesis of DNA. These results suggest that the reduction in the intracellular levels of prolactin are a primary event in the oestrogen mediated stimulation of cell proliferation by prolactin releasing agents.

DNA polymerases in the rat pituitary gland. Effect of oestrogens and sulpiride

Changes in the activity of DNA polymerase and [3H]thymidine incorporation into the DNA of the anterior pituitary gland were studied in oestrogenized male and pregnant rats. The activities of DNA polymerases alpha and beta, extracted in Tris--HCl or in sodium phosphate buffer were characterized according to their optimum pH and sensitivity to N-ethyl-maleimide. In the Tris-soluble fraction DNA polymerase activity is almost exclusively alpha, while in the phosphate soluble fraction it is a mixture of alpha and beta. The administration of oestrogens to male rats increases [3H]thymidine incorporation and enhances the activity of DNA polymerases in the Tris-soluble fraction, while the activity of the phosphate-soluble enzyme does not change. Sulpiride administration results in a further increment of [3H]thymidine incorporation and of DNA polymerase activity in the Tris-soluble fraction. In pregnant rats sulpiride also produces an increment of DNA polymerase activity only in the Tris-soluble fraction. Thus, the activity of the Tris-soluble fraction from APG behaves as DNA polymerase alpha. This activity changes in parallel with [3H]thymidine incorporation into DNA which is an indication of cell proliferation in the gland. This is discussed with respect to a negative feedback mechanism between intracellular prolactin concentration and DNA synthesis in the APG.

DNA synthesis in the pituitary gland of the rat: effect of sulpiride and clomiphene

Sulpiride administration to rats releases prolactin and increases DNA replication in the anterior pituitary gland. Clomiphene prevents the stimulation of DNA synthesis produced by sulpiride, but does not affect prolactin release from the gland. These findings suggest that the intracellular prolactin content of the anterior pituitary gland plays a role in the regulation of DNA synthesis through a mechanism mediated by oestrogens.

DNA synthesis in the pituitary gland of the rat. Effect of sulpiride and postnatal maturation

During development of the rat anterior pituitary gland (APG) there is a fall in DNA replication which is accompanied by a decline in the activity of the soluble DNA polymerase and of an endonuclease. This latter enzyme is capable of activating the DNA template for the DNA polymerase assay. Sulpiride sulfate, a drug known to produce prolactin release from the APG, increases thymidine incorporation in the APG 20 h after the injection. This drug also enhances the activity of the soluble DNA polymerase while that of the endonuclease and thymidine kinase does not change. The results suggest that the intracellular prolactin content regulates DNA replication in mammotrophs and that the soluble DNA polymerase plays an important role in this regulation.