Hormonal measurement in rat anterior pituitary cell cultures: loss of immunoreactive LH counteracted by fetal calf serum and bacitracin

Measurement of serum and plasma osmolality in healthy young humans – influence of time and storage conditions

Background: The precise measurement of osmolality is crucial in the differential diagnosis of disorders of water balance. Storage conditions, and freezing and thawing of serum or plasma samples before osmometry may influence the accuracy of measured values. Methods: A series of serum and plasma samples of 25 healthy young individuals were stored under different conditions at different temperatures (room temperature (22°C), 7°C, –21°C, –78°C) for up to 56 days. Before freezing a protein-stabilizing agent (bacitracin) was added to one part of the samples. Osmolality was examined using the freezing point method. Results: At room temperature osmolality was stable for up to 3 days but showed a tendency toward an increase that was significant on day 14. In contrast, at 7°C an initial significant decrease in serum osmolality occurred (day 1), which was followed by a slow increase. Serum samples stored at –21°C showed a significantly lower osmolality on the 14th day compared to baseline. Adding bacitracin before freezing reduced this decrease by more than half, but the deviation was still significant. In samples stored at –78°C no significant alteration of osmolality from baseline was observed over the observation period of 56 days if samples were thawed in a 37°C water bath. Conclusion: Immediate measurement of osmolality is most reliable in order to obtain accurate values, although storing at room temperature does not influence osmolality significantly during the first 3 days. If storage is necessary for longer, samples should be stored at –78°C and must be thawed quickly (at 37°C). Under these conditions reliable values can be obtained from frozen serum or plasma. Storage at 7°C is not recommended. If samples are stored at –21°C the addition of a protein-stabilizing agent may be useful.

Alcohol effects on TRH-induced prolactin response in lactating rats: in vivo and in vitro studies

The site of action of alcohol in inhibiting suckling-induced prolactin release in lactating rats was examined by in vivo and in vitro studies. In vivo, sulpiride- and thyrotropin-releasing hormone (TRH)-induced prolactin release was studied in lactating rats separated from their litter. On day 7, dams were implanted with an atrial catheter. On day 10, pups were removed from dams at 0800 h and, after 5 h, an extension was attached to the catheter. An hour later, a baseline blood sample was removed and was followed by sulpiride (40 micrograms/kg) administration. Additional blood samples were withdrawn over 1 h. After the 60-min sample, sulpiride-administered rats were infused with 0.0, 1.0, or 2.0 g/kg b.wt. alcohol. Following alcohol, a postinfusion blood sample was removed, TRH (4.0 micrograms/kg) was administered, and subsequent blood samples were obtained 5, 10, 20, and 30 min after TRH. For in vitro studies, cells from lactating rats in midlactation were enzymatically dissociated, plated, and on culture day 5 were exposed to 0 or 10 nM TRH. Each set of cells were additionally exposed to 0, 100, or 300 mg% alcohol and media harvested after 4 h. In a subsequent study, plated cells were exposed to increasing doses of TRH in the presence of 0, 100, or 300 mg% alcohol and media harvested as above. Prolactin in plasma (in vivo studies) and medium (in vitro studies) was measured by RIA.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of charcoal-extracted follicular fluid on reproductive function in postpartum cows

In order to determine the role of follicle-stimulating hormone (FSH) on the resumption of ovarian function in cows early postpartum (PP), bovine follicular fluid (FF) was used to selectively suppress concentrations of FSH. Calves were removed from all cows within 24 hr of birth. Follicular fluid that was treated with charcoal to remove steroids (15 ml; n = 14) or serum (S) from an ovariectomized cow (15 ml, n = 14) was injected i.m. twice daily from days 1 to 10 PP. Blood samples were collected before each injection and frequent samples (every 15 min for 6 hr) taken on days 5 and 10 PP. Eight cows from each group (FF and S) were slaughtered on the morning of day 11 PP and pituitaries and ovaries collected. The remaining cows (n = 6) were observed for estrus. Treatment with FF delayed follicular growth (P less than 0.01), as evidenced by the largest follicle per cow observed at time of slaughter (3.6 +/- 0.42 vs 11.5 +/- 1.77 mm dia; FF vs S). The intervals from parturition to first estrus (P less than 0.11) and to first progesterone rise (25.3 +/- 1.97 vs 18.0 +/- 3.62 d; P less than 0.06) tended to be delayed by treatment with FF vs S. Many of the cows treated with S ovulated by day 10 PP, they were divided retrospectively into those that had ovulated by (n = 9) or after (n = 5) day 10 PP for analysis. Cows treated with FF had lower (P less than 0.05) and less variable (P less than 0.01) serum FSH concentrations while levels of luteinizing hormone (LH) tended (P less than 0.08) to be greater on days 5 and 10 PP. Follicular fluid decreased levels of FSH (P less than 0.001), but not LH (P less than 0.15), in the samples obtained twice daily compared to S-treated cows that did not ovulate by day 10 PP. Anterior pituitaries were dissociated, and cells from each cow were cultured in order to ascertain whether treatment with FF in vivo would affect gonadotropin secretion in vitro. Estradiol-17 beta (E) was incubated with pituitary cells to determine the effect of E on gonadotropin secretion from cells of PP cows, and to ascertain whether treatment with FF in vivo and with E in vitro would interact to affect secretion of FSH and LH in culture. After 2 d of incubation, cells were treated with 10(-9) M E or vehicle (1% ethanol).(ABSTRACT TRUNCATED AT 400 WORDS)

Estrogenic effects of phenol red on rat pituitary cell responsiveness to gonadotropin-releasing hormone

This study investigated whether phenolsulfonphthalein (PR), a common pH indicator in tissue culture media, affects luteinizing hormone (LH) secretion from rat pituitary cells or 17 beta-estradiol (E2) augmentation of pituitary responsiveness to gonadotropin-releasing hormone (GnRH). PR enhanced GnRH-stimulated LH secretion and shifted the GnRH dose-response curve leftward with a relative potency ratio of 0.24 +/- 0.09 (+/- SE; p less than 0.01). The effect of E2 on LH release was significantly diminished by PR, which elevated GnRH-stimulated LH secretion in the absence of E2. This phenomenon was elicited by PR from different sources and was inhibited by the antiestrogen Cl628. Thus, PR exerted estrogen-like effects on rat pituitary cells and caused an underestimation of the degree to which E2 enhanced GnRH-stimulated LH secretion.

Pituitary gonadotropin content in gonadectomized rats. Immunoassay measurements influenced by extraction solvent and testosterone replacement

Increasing interest in events regulating gonadotropin synthesis and secretion led to the reexamination, by radioimmunoassay (RIA), of the pituitary content of luteinizing hormone (LH) and follicle stimulating hormone (FSH). In a preliminary experiment, the importance of the composition of the solvent used to homogenize pituitaries on the detection of LH and FSH was demonstrated by RIA. Experiment 1 demonstrated that a drop in pituitary FSH occurred acutely following gonadectomy in males, but not in females. Experiment 2 tested whether this decline resulted from loss of testosterone or inhibin. Males were castrated and treated daily with oil or testosterone propionate, porcine follicular fluid, porcine serum, or testosterone plus follicular fluid for 2 to 14 days. Castration lowered pituitary FSH at 2, 4, and 6 days. Follicular fluid suppressed serum FSH, but not LH, and did not prevent the fall in pituitary FSH. Testosterone blocked the rise of serum LH and FSH and prevented the decline in pituitary FSH.

Superfused pituitary cell cultures: effects of culture conditions on apparent responsiveness to LHRH stimulation administered as short duration pulses

We wished to study estrous cycle related differences in LH and FSH responsiveness to pulsatile LHRH. Such studies are very difficult to perform in vivo under controlled conditions; therefore, an in vitro superfused anterior pituitary cell culture system was evaluated for its capacity to support differences in estrous stage associated LHRH responsiveness. Three vital culture system parameters were evaluated; these parameters were (1) culture medium composition, (2) duration allowed for cell attachment to microcarrier beads and (3) superfusion flow rate utilized during pulsatile LHRH stimulation. It was found that a culture system which utilized 10% Nu Serum in DMEM (final protein concentration of 1.8 mg/ml; final serum concentration of 2.5%), an attachment time of 48 hrs and a flow rate of 0.125 ml/min most successfully maximized LH responsiveness at the lowest serum concentration. These studies indicated that although one may be able to observe LHRH responsiveness under a wide range of culture conditions, responsiveness may nonetheless be maximized by judicious adjustment of culture conditions.

Enzymatic tracer damage during the gonadotropin releasing hormone radioimmunoassay: analytical and immunological assessment

Hypothalamic supernatants from 60 day female rats were fractionated from Sephadex G-200 columns. The radioimmunoassay (RIA) for gonadotropin releasing hormone (GnRH) detected an apparently cross-reacting high molecular weight substance. The substance caused apparent displacement of iodinated GnRH binding in dose response fashion; however, no biological activity was observed in pituitary cell cultures. In order to determine whether the depressed binding might be caused by enzymatic degradation of iodinated GnRH during the RIA incubation, iodinated GnRH was preincubated under RIA conditions with either buffer or increasing concentrations of the GnRH cross-reacting material. Aliquots were subjected to polyacrylamide gel electrophoresis (PAGE) and the gels slices counted. Identical aliquots were subsequently used as iodinated hormone in the RIA of known quantities of synthetic GnRH. Tracer damage during the RIA-like preincubation period was reflected in the subsequent PAGE studies as decreased counts per minute in the intact GnRH peak and in the RIA studies as over-estimated quantification of the GnRH standards. This report describes such damage during the GnRH RIA and the data misinterpretations which result.

LHRH inactivation by reconstituted horse and fetal bovine sera: assessment by reduction of immunoreactivity and biological activity in pituitary cell cultures

Lyophilized horse and fetal bovine sera are commonly incorporated into the growth media used for primary pituitary cell cultures. LHRH degrading activity has been assumed to exist in these preparations but has not actually been demonstrated. During our studies with pituitary cultures, it became necessary to ascertain if LHRH inactivating activity could be demonstrated in these sera. Luteinizing hormone releasing hormone (LHRH) was preincubated in either serum-free medium or medium containing fetal bovine and horse serum. Whether LHRH was lost during these incubations was assessed by diminished immunoreactivity as indicated by radioimmunoassay (RIA) and by diminished biological activity as indicated by reduced release of LH from pituitary cell cultures. Both the RIA and bioassay results indicated LHRH inactivating activity; the loss of LHRH could be prevented by inclusion of bacitracin in the incubations.

Intracellular receptors mediate gonadal steroid modulation of LHRH-induced LH release

Primary cultures of enzymatically dispersed rat pituitary cells were used to study the role of intracellular receptors in gonadal steroid modulation of LHRH-induced LH release. Nuclear receptors for both testosterone (T) and 17 beta-estradiol (E) were observed, with KD values of 6.3 and 0.1 nM respectively. Occupation of these receptors was correlated with modulation of LH secretion. The relationship between these two parameters was nonlinear, so that steroid effects on LH secretion were maximal when fewer than 50% of the receptors were occupied. The androgen antagonist cyproterone blocked both T binding to nuclear receptors and T inhibition of LH secretion. Similarly, the estrogen antagonist CI-628 blocked both E binding and E stimulation of LH secretion. In cultures derived from pseudohermaphrodite rats. T did not bind to nuclear receptors, nor did it inhibit LH secretion. These results, showing a relationship between occupation of nuclear receptors and modulation of LH secretion, suggest that steroid effects on LH secretion are mediated by these receptors.

Gonadal steroid modulation of LHRH-stimulated LH secretion by pituitary cell cultures

Enzymatically dispersed rat pituitary cells were grown in primary culture, and LHRH-stimulated LH secretion was measured. Testosterone (T) decreased and 17 beta-estradiol (E) increased pituitary responsiveness to LHRH. The effect of E on LH secretion was partly due to an increase in LH content. There was a latent period of 12 h for E and 18 h for T between the onset of steroid treatment and the manifestation of steroid action. Neither steroid was required to be continuously present in order to exert its effects. After steroid withdrawal, the effect of T persisted for 72 h and that of E for more than 96 h. The actions of both steroids were blocked by protein-synthesis inhibitors. These results are consistent with the hypothesis that steroid effects rely on a mechanism involving alterations in protein synthesis; the affected proteins may be involved in the process of LHRH action.