Pituitary-brain vascular relations: a new paradigm

The interaction of MC3R and MC4R with MRAP2, ACTH, α-MSH and AgRP in chickens

The interaction of melanocortin-4 (MC4R) and melanocortin-3 (MC3R) receptors with proopiomelanocortin (POMC)-derived peptides (e.g. α-MSH), agouti-related protein (AgRP) and melanocortin-2 receptor accessory protein 2 (MRAP2) is suggested to play critical roles in energy balance of vertebrates. However, evidence on their interaction in birds remains scarce. Our study aims to reveal their interaction in chickens and the results showed that (1) chicken (c-)MC3R and cMC4R expressed in Chinese hamster ovary (CHO) cells can be activated by α-MSH and ACTH_1-39 equipotently, monitored by a pGL3-CRE-luciferase reporter system; (2) cMC3R and cMC4R, when co-expressed with cMRAP2 (or cMRAP, a cMRAP2 homolog), show increased sensitivity to ACTH treatment and thus likely act as ACTH-preferring receptors, and the interaction between cMC3R/cMC4R and cMRAP2 was demonstrated by co-immunoprecipitation assay; (3) both cMC3R and cMC4R display constitutive activity when expressed in CHO cells, as monitored by dual-luciferase reporter assay, and cMRAP2 (and cMRAP) can modulate their constitutive activity; (4) AgRP inhibits the constitutive activity of cMC3R/cMC4R, and it also antagonizes ACTH/α-MSH action on cMC4R/cMC3R, indicating that AgRP functions as the inverse agonist and antagonist for both receptors. These findings, together with the co-expression of cMC4R, cMC3R, cMRAP2, cAgRP and cPOMC in chicken hypothalamus detected by quantitative real-time PCR, suggest that within the hypothalamus, α-MSH/ACTH, AgRP and MRAP2 may interact at the MC4R(/MC3R) interface to control energy balance. Furthermore, our data provide novel proof for the involvement of MRAP2 (and MRAP) in fine-tuning the constitutive activity and ligand sensitivity and selectivity of both MC3R and MC4R in vertebrates.

Pterostilbene Decreases the Antioxidant Defenses of Aggressive Cancer Cells In Vivo: A Physiological Glucocorticoids- and Nrf2-Dependent Mechanism

AIMS

Polyphenolic phytochemicals have anticancer properties. However, in mechanistic studies, lack of correlation with the bioavailable concentrations is a critical issue. Some reports had suggested that these molecules downregulate the stress response, which may affect growth and the antioxidant protection of malignant cells. Initially, we studied this potential underlying mechanism using different human melanomas (with genetic backgrounds correlating with most melanomas), growing in nude mice as xenografts, and pterostilbene (Pter, a natural dimethoxylated analog of resveratrol).

RESULTS

Intravenous administration of Pter decreased human melanoma growth in vivo. However, Pter, at levels measured within the tumors, did not affect melanoma growth in vitro. Pter inhibited pituitary production of the adrenocorticotropin hormone (ACTH), decreased plasma levels of corticosterone, and thereby downregulated the glucocorticoid receptor- and nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-dependent antioxidant defense system in growing melanomas. Exogenous corticosterone or genetically induced Nrf2 overexpression in melanoma cells prevented the inhibition of tumor growth and decreased antioxidant defenses in these malignant cells. These effects and mechanisms were also found in mice bearing different human pancreatic cancers. Glutathione depletion (selected as an antimelanoma strategy) facilitated the complete elimination by chemotherapy of melanoma cells isolated from mice treated with Pter.

INNOVATION

Although bioavailability-related limitations may preclude direct anticancer effects in vivo, natural polyphenols may also interfere with the growth and defense of cancer cells by downregulating the pituitary gland-dependent ACTH synthesis.

CONCLUSIONS

Pter downregulates glucocorticoid production, thus decreasing the glucocorticoid receptor and Nrf2-dependent signaling/transcription and the antioxidant protection of melanoma and pancreatic cancer cells. Antioxid. Redox Signal. 24, 974-990.

Recent insights into the cell biology of thyroid angiofollicular units

In thyrocytes, cell polarity is of crucial importance for proper thyroid function. Many intrinsic mechanisms of self-regulation control how the key players involved in thyroid hormone (TH) biosynthesis interact in apical microvilli, so that hazardous biochemical processes may occur without detriment to the cell. In some pathological conditions, this enzymatic complex is disrupted, with some components abnormally activated into the cytoplasm, which can lead to further morphological and functional breakdown. When iodine intake is altered, autoregulatory mechanisms outside the thyrocytes are activated. They involve adjacent capillaries that, together with thyrocytes, form the angiofollicular units (AFUs) that can be considered as the functional and morphological units of the thyroid. In response to iodine shortage, a rapid expansion of the microvasculature occurs, which, in addition to nutrients and oxygen, optimizes iodide supply. These changes are triggered by angiogenic signals released from thyrocytes via a reactive oxygen species/hypoxia-inducible factor/vascular endothelial growth factor pathway. When intra- and extrathyrocyte autoregulation fails, other forms of adaptation arise, such as euthyroid goiters. From onset, goiters are morphologically and functionally heterogeneous due to the polyclonal nature of the cells, with nodules distributed around areas of quiescent AFUs containing globules of compact thyroglobulin (Tg) and surrounded by a hypotrophic microvasculature. Upon TSH stimulation, quiescent AFUs are activated with Tg globules undergoing fragmentation into soluble Tg, proteins involved in TH biosynthesis being expressed and the local microvascular network extending. Over time and depending on physiological needs, AFUs may undergo repetitive phases of high, moderate, or low cell and tissue activity, which may ultimately culminate in multinodular goiters.

The pathogenesis of pituitary tumors

Recently there has been significant progress in our understanding of pituitary development, physiology, and pathology. New information has helped to clarify the classification of pituitary tumors. Epidemiologic analyses have identified a much higher incidence of pituitary tumors than previously thought. We review the pathogenetic factors that have been implicated in pituitary tumorigenesis and the application of novel targeted therapies that underscore the increasingly important role of the pathologist in determining accurate diagnoses and facilitating appropriate treatment of patients with these disorders.

Differences in the Peripheral Levels of ??-endorphin in Response to Alcohol and Stress as a Function of Alcohol Dependence and Family History of Alcoholism

BACKGROUND

Evidence indicates that both genetic and environmental factors, such as stress, may play an important role for the development of alcoholism, while beta-endorphin may be implicated in the control of alcohol consumption. The objective of the present studies was to test the hypothesis that there are differences in the response of the pituitary beta-endorphin system to stress as a function of family history of alcoholism and alcohol dependence.

METHODS

The response of the pituitary beta-endorphin to a placebo or an alcohol (0.50 g ethanol/kg) drink and to a stress task performed 30 min following ingestion of either the placebo or the alcohol drink was measured in social and heavy drinkers with [high risk (HR)] and without [low risk (LR)] a family history of alcoholism. Thus, each subject participated in 4 experimental sessions given on different days in a randomized order. Four groups of subjects were investigated: 1) low risk nonalcoholics (LRNA); 2) high risk nonalcoholics (HRNA), 3) low risk alcoholics (LRA); and 4) high risk alcoholics (HRA). Plasma beta-endorphin was estimated prior to and for 3.5 hr post-stress. Changes in the concentration of plasma beta-endorphin following ingestion of either the placebo or alcohol drink without performance of the stress task served as controls to compare the stress-induced changes.

RESULTS

Basal plasma beta-endorphin levels were higher in LRNA than LRA, HRNA and HRA participants, while basal plasma beta-endorphin levels were higher in LRA than those in HRNA and HRA participants. Furthermore, there was no significant difference in the plasma beta-endorphin levels between HRNA and HRA participants. Stress, induced a significant increase in plasma beta-endorphin concentration in all four groups of participants. However, the stress-induced increase in plasma beta-endorphin levels was more pronounced in LRNA than HRNA, LRA and HRA participants. Thus, alcohol dependence decreased the basal plasma beta-endorphin levels in LR only, as well as the stress induced increase in plasma beta-endorphin levels of participants without, but not of those with, a family history of alcoholism. Alcohol prior to stress attenuated the stress-induced increase in plasma beta-endorphin levels of all four groups of participants.

CONCLUSIONS

The present data indicates that there are differences in both, the basal plasma beta-endorphin levels as well as the response of the pituitary beta-endorphin to stress as a function of family history of alcoholism and alcohol dependence. Thus, in HR individuals a dysfunction in the activity of the pituitary beta-endorphin system predates the development of alcoholism, while in LR individuals it develops following alcohol dependence. Furthermore, alcohol dependence did not alter the alcohol-induced attenuation of beta-endorphin response to stress.

Sodium vitamin C cotransporter SVCT2 is expressed in hypothalamic glial cells

Kinetic analysis of vitamin C uptake demonstrated that different specialized cells take up ascorbic acid through sodium-vitamin C cotransporters. Recently, two different isoforms of sodium-vitamin C cotransporters (SVCT1/SLC23A1 and SVCT2/SLC23A2) have been cloned. SVCT2 was detected mainly in choroidal plexus cells and neurons; however, there is no evidence of SVCT2 expression in glial and endothelial cells of the brain. Certain brain locations, including the hippocampus and hypothalamus, consistently show higher ascorbic acid values compared with other structures within the central nervous system. However, molecular and kinetic analysis addressing the expression of SVCT transporters in cells isolated from these specific areas of the brain had not been done. The hypothalamic glial cells, or tanycytes, are specialized ependymal cells that bridge the cerebrospinal fluid with different neurons of the region. Our hypothesis postulates that SVCT2 is expressed selectively in tanycytes, where it is involved in the uptake of the reduced form of vitamin C (ascorbic acid), thereby concentrating this vitamin in the hypothalamic area. In situ hybridization and optic and ultrastructural immunocytochemistry showed that the transporter SVCT2 is highly expressed in the apical membranes of mouse hypothalamic tanycytes. A newly developed primary culture of mouse hypothalamic tanycytes was used to confirm the expression and function of the SVCT2 isoform in these cells. The results demonstrate that tanycytes express a high-affinity transporter for vitamin C. Thus, the vitamin C uptake mechanisms present in the hypothalamic glial cells may perform a neuroprotective role concentrating vitamin C in this specific area of the brain.

Acupuncture for chronic prostatitis/ chronic pelvic pain syndrome

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is prevalent in urological practice and has a significant impact on quality of life. Standard therapies often fail to achieve sustainable amelioration of symptoms. This article attempts to show that neuromodulatory treatment in the form of electroacupuncture can be a minimally invasive and effective treatment for CP/CPPS that is refractory to standard therapies. This neuromodulatory therapy lends support to the hypothesis that the end stage of CP/CPPS may be a neuropathic pain syndrome.

Delineation of responsive AVP-containing neurons to running stress in the hypothalamus

Running becomes a stress, termed running stress, if it persists above the lactate threshold (LT) and results in enhanced plasma ACTH level in humans. Although the exact underlying regulation mechanism is still uncertain, hypothalamic AVP has been shown to play a dominant role in running-induced ACTH release. It is still not known, however, whether running stress activates the hypothalamic AVP-containing neurons that are involved in the activation of the ACTH response. For this reason, we applied our rat running stress model, in which both plasma ACTH and osmolality levels increase just above LT running (supra-LT running), to delineate which hypothalamic AVP neurons were responsive to running stress. Rats were previously habituated to running and then subjected to a 30-min run either just below or above the LT. Plasma samples were collected from these animals to determine ACTH and osmolality levels. Brains were prepared for immunocytochemistry for both AVP/Fos in the hypothalamus and enzyme immunoassay for the stalk median eminence (SME) AVP content. Only supra-LT running resulted in an increase in the number of Fos/AVP-immunoreactive neurons in both the parvocellular paraventricular nucleus (pPVN) and the magnocellular supraoptic nucleus (SON) accompanied by increased ACTH and plasma osmolality levels. Similarly, running reduced the SME content of the AVP. We thus found that AVP-containing neurons located in both the pPVN and SON are responsive to running stress just above the LT.

Angiogenesis in endocrine tumors

Angiogenesis is the process of new blood vessel development from preexisting vasculature. Although vascular endothelium is usually quiescent in the adult, active angiogenesis has been shown to be an important process for new vessel formation, tumor growth, progression, and spread. The angiogenic phenotype depends on the balance of proangiogenic growth factors such as vascular endothelial growth factor (VEGF) and inhibitors, as well as interactions with the extracellular matrix, allowing for endothelial migration. Endocrine glands are typically vascular organs, and their blood supply is essential for normal function and tight control of hormone feedback loops. In addition to metabolic factors such as hypoxia, the process of angiogenesis is also regulated by hormonal changes such as increased estrogen, IGF-I, and TSH levels. By measuring microvascular density, differences in angiogenesis have been related to differences in tumor behavior, and similar techniques have been applied to both benign and malignant endocrine tumors with the aim of identification of tumors that subsequently behave in an aggressive fashion. In contrast to other tumor types, pituitary tumors are less vascular than normal pituitary tissue, although the mechanism for this observation is not known. A relationship between angiogenesis and tumor size, tumor invasiveness, and aggressiveness has been shown in some pituitary tumor types, but not in others. There are few reports on the role of microvascular density or angiogenic factors in adrenal tumors. The mechanism of the vascular tumors, which include adrenomedullary tumors, found in patients with Von Hippel Lindau disease has been well characterized, and clinical trials of antiangiogenic therapy are currently being performed in patients with Von Hippel Lindau disease. Thyroid tumors are more vascular than normal thyroid tissue, and there is a clear correlation between increased VEGF expression and more aggressive thyroid tumor behavior and metastasis. Although parathyroid tissue induces angiogenesis when autotransplanted and PTH regulates both VEGF and MMP expression, there are few studies of angiogenesis and angiogenic factors in parathyroid tumors. An understanding of the balance of angiogenesis in these vascular tumors and mechanisms of vascular control may assist in therapeutic decisions and allow appropriately targeted treatment.

Hypothalamic ependymal-glial cells express the glucose transporter GLUT2, a protein involved in glucose sensing

The GLUT2 glucose transporter and the K-ATP-sensitive potassium channels have been implicated as an integral part of the glucose-sensing mechanism in the pancreatic islet beta cells. The expression of GLUT2 and K-ATP channels in the hypothalamic region suggest that they are also involved in a sensing mechanism in this area. The hypothalamic glial cells, known as tanycytes alpha and beta, are specialized ependymal cells that bridge the cerebrospinal fluid and the portal blood of the median eminence. We used immunocytochemistry, in situ hybridization and transport analyses to demonstrate the glucose transporters expressed in tanycytes. Confocal microscopy using specific antibodies against GLUT1 and GLUT2 indicated that both transporters are expressed in alpha and beta tanycytes. In addition, primary cultures of mouse hypothalamic tanycytes were found to express both GLUT1 and GLUT2 transporters. Transport studies, including 2-deoxy-glucose and fructose uptake in the presence or absence of inhibitors, indicated that these transporters are functional in cultured tanycytes. Finally, our analyses indicated that tanycytes express the K-ATP channel subunit Kir6.1 in vitro. As the expression of GLUT2 and K-ATP channel is linked to glucose-sensing mechanisms in pancreatic beta cells, we postulate that tanycytes may be responsible, at least in part, for a mechanism that allows the hypothalamus to detect changes in glucose concentrations.

Effect of chronic alcohol consumption on the activity of the hypothalamic-pituitary-adrenal axis and pituitary beta-endorphin as a function of alcohol intake, age, and gender

BACKGROUND

Experimental evidence indicates that components of the hypothalamic-pituitary-adrenal (HPA) axis and of the endogenous opioid system, such as beta-endorphin (beta-END), influence alcohol consumption, whereas chronic alcohol abuse alters the activity of both systems. Furthermore, gender and age differences have been reported in the activity of the HPA axis under basal conditions, in response to stress and acute alcohol challenge. The objective of the present studies was to investigate the hypothesis that chronic alcohol consumption alters the activity of the HPA axis and pituitary beta-END as a function of severity of alcohol abuse, gender, and age.

METHODS

Three age groups of each gender (18-29, 30-44, and 45-60 years old) were recruited. Each age and gender group included four subgroups: (a) nondrinkers, (b) light drinkers, (c) heavy drinkers, and (d) alcoholics in treatment. Demographic characteristics, alcohol consumption, and presence of alcohol dependence were recorded by using a structured interview. Blood samples were taken on the day of the interview. The levels of plasma adrenal corticotropic hormone (ACTH), cortisol, and beta-END were estimated as an index of the activity of the HPA-axis and pituitary beta-END.

RESULTS

Plasma ACTH and beta-END levels were significantly lower in females than males of all age and drinking category groups. Plasma cortisol levels were higher in 18- to 29-year-old female subjects compared with the 18- to 29-year-old male subjects. The plasma ACTH and beta-END levels were lower whereas plasma cortisol levels were higher in heavy drinkers than nondrinkers. This decrease in plasma ACTH and beta-END levels with heavy drinking was more pronounced in female than male subjects of the 30-44 and 45-60 age groups.

CONCLUSIONS

Chronic drinking, gender, and age influence the activity of the HPA-axis and pituitary beta-END, which in turn may influence drinking behavior.

Pituitary surgery complicated by haemorrhagic necrosis of residual tumour

Haemorrhagic necrosis of residual pituitary tumour following partial excision has not previously been well described. This is differentiated from post-operative sellar haematoma due to inadequate haemostasis on the basis of absent free clot. The authors report two cases of large macroadenomas with significant supra-sellar extension which were complicated by haemorrhagic necrosis of residual tumour following initial surgery. The literature is reviewed and possible pathophysiogical mechanisms are discussed.

The effect of the alpha-2-adrenergic agonist, clonidine, on secretion patterns and rates of adrenocorticotropic hormone and its secretagogues in the horse

Alpha-2-adrenoceptor activation may lower adrenocorticotropic hormone (ACTH) by reducing secretagogue input and/or increasing the release of an inhibitory factor (CIF). To investigate this, we gave clonidine, an alpha-2-agonist, to seven horses, and collected pituitary venous blood every minute for 20 min before treatment and 40 min after treatment. Six horses were given saline vehicle. Mean secretion rates of corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP) and ACTH were calculated before and during four 5-min then two 10-min periods after clonidine or saline. Reduction in ACTH secretion without corresponding changes in CRH and/or AVP would imply the presence of CIF. Secretion rates of ACTH (P = 0.008) and AVP (P = 0.0005) fell after clonidine and remained lower than baseline values for 20 min and 10 min, respectively. The CRH secretion rate decreased slightly but not significantly after clonidine. In controls, hormone secretion rates did not alter during the experiment. Multiple linear regression showed that CRH and AVP secretion accounted for 69% (treated) or 45% (controls) of the variation in ACTH secretion (P < 0.0001 for each). CRH alone contributed 80% (treated) or 76% (controls) of the fit to this model, which is consistent with the concept that CRH 'sets the gain' of the response of corticotrophs to fluctuations in AVP. Accordingly, minute-to-minute changes in pituitary concentrations of AVP and ACTH were synchronous when all data were considered (% concordant changes: controls, 68%, P < 0.0001; treated, 76%, P < 0.0001) and the percentage of concordant movement was unaffected by clonidine (before 72%; after 73%; P = 0.80). In treated horses but not controls, the ratio between the secretion rates of ACTH and AVP fell (P = 0.009), while the ACTH : CRH ratio tended to fall after clonidine, implying reduced responsiveness to stimulation. Moreover, one horse showed a drop in ACTH and a rise in CRH and AVP secretion after clonidine. We conclude that in horses alpha-2-adrenoceptor activation lowers ACTH secretion primarily by reducing the secretion of AVP and possibly CRH. While there was some evidence that a CIF may participate in the clonidine-induced suppression of ACTH, the subtlety of the discordance between ACTH and its secretagogues in most horses and the rarity of complete dissociation indicate that it does not play a major role.

The pituitary gland: embryology, physiology, and pathophysiology

The pituitary gland, the "master gland" of the body, is composed of endocrine cells, which secrete hormones essential for homeostasis. The gland consists of the adenohypophysis (anterior pituitary) and the neurohypophysis (posterior pituitary), two unique structures that differ anatomically and functionally. The neurohypophysis is innervated by nerve cells in the hypothalamus and forms the connection between it and the pituitary gland. The hypothalamus stimulates release and inhibition of pituitary hormones. The neurohypophysis secretes oxytocin and antidiuretic hormone. The adenohypophysis is composed of three structures: the pars distalis, the pars intermedia, and the pars tuberalis. The anterior pituitary (pars distalis) is responsible for the release of hormones that include growth hormone, prolactin, thyroid-stimulating hormone, follicle-stimulating hormone, luteinizing hormone, adrenocorticotropic hormone, and melanocyte-stimulating hormone. Disorders of the pituitary are predominately those of insufficient hormone release and may have profound effects on the neonate. The potential causes of and clinical symptomatology that may accompany pituitary hormone insufficiency in the neonatal period are explored.

MK-801-induced disruptions of one-trial inhibitory avoidance are potentiated by stress and reversed by naltrexone

Five experiments were carried out to investigate opioid and NMDA receptor-mediated responses to one-trial inhibitory avoidance training in CD1 mice. In the first experiment immediate posttraining intraperitoneal administration of the noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 impaired the performance of mice. The effects of MK-801 were time-dependent (they were absent in mice injected with the drug starting 120 min after training). No effect was evident in no-foot-shock groups, showing lack of proactive influence of the treatment on performance. In the second experiment preexposure of the mice to the testing apparatus decreased the effects of MK-801. In the the third experiment naltrexone antagonized the effects of MK-801, suggesting an involvement of opioid neurons. In the fourth experiment immediate posttraining immobilization stress exerted a potentiating effect on the performance of MK-801-injected animals. In the fifth experiment the potentiation of the impairing effect of MK-801 induced by immobilization stress was antagonized by naltrexone.

High intensity exercise promotes escape of adrenocorticotropin and cortisol from suppression by dexamethasone: sexually dimorphic responses

Exercise promotes escape of ACTH and cortisol from suppression by dexamethasone (DEX) in some healthy men and women. To determine whether stimulus strength, diurnal rhythmicity, or gender influences neuroendocrine escape during DEX suppression, we studied men (n = 5) and women (n = 5) during high intensity exercise tests after taking 4 mg DEX: two tests (one at 90% and one at 100% of maximal aerobic capacity) were conducted in the morning and two were performed in the afternoon on nonconsecutive days. Plasma ACTH and cortisol showed significantly greater increases with the 100% compared to the 90% intensity exercise (ACTH: 90%, 2 +/- 0.4; 100%, 3 +/- 0.5 pmol/L; cortisol: 90%, 53 +/- 5.3; 100% 93 +/- 23.6 nmol/L). Plasma cortisol responses were significantly higher in women than in men (P < 0.01). Plasma arginine vasopressin (AVP) exhibited significant intensity-dependent increases, with higher responses in women than men (P < 0.01). In conclusion, despite high dose glucocorticoid pretreatment, intense exercise can override the glucocorticoid negative feedback of hypothalamic-pituitary-adrenal activation in most normal men and women. This ability to override cortisol negative feedback inhibition may relate to the magnitude of the AVP response, the potency/specificity of the stressor to elicit a CRH/AVP response, and/or the sensitivity of the glucocorticoid negative feedback system at the time of the stress.

Evidence for diverse pathways of hypophysiotropic hormone transport in mammals

Comparative studies of mammalian hypothalamic-pituitary relationships have revealed striking variations in hypophysiotropic systems and in portal vascular architecture. Immunocytochemical studies indicate that mammalian GnRH, GHRH and somatostatin systems can project to all portions of the neurohypophysis (median eminence, infundibular stem and pituitary neural lobe). In rats, primary secretion sites are located within the median eminence and upper infundibular stem, whereas in bats, most projections extend into the lower infundibular stem and pituitary neural lobe. In ferrets and monkeys, sites of secretion appear to extend throughout the neurohypophysis, from median eminence to proximal neural lobe. In this review, these interspecific differences are examined in light of observed structural variations in portal vascular systems. Correlations suggest that hypophysiotropic hormones can be delivered to target cells in the pars distalis by diverse routes, with some species relying more heavily on long and others on short portal transport. These patterns may have important functional implications with respect to regulatory mechanisms operating within the hypothalamic-pituitary complex.

Fetal ethanol exposure: hypothalamic-pituitary-adrenal and beta-endorphin responses to repeated stress

Previous studies provide evidence that fetal ethanol exposure induces hypothalamic-pituitary-adrenal (HPA) and pituitary beta-endorphin (beta-EP) hyperresponsiveness to acute stressors. The present study demonstrates significant effects of in utero ethanol exposure on the parallel response patterns of the HPA axis and the pituitary beta-EP system to repeated exposures to a stressor, restraint stress, and indicates sex differences in response. Together, data from the two experiments indicate that, after repeated restraint exposures, fetal ethanol-exposed (E) males and females both show significantly increased plasma levels of adrenocorticotropin (ACTH), and E males also show significantly increased plasma levels of beta-endorphin-like immunoreactivity (beta-EPLIR), compared with their respective pair-fed and control counterparts. Marginal increases in the corticosterone response of E males and the beta-EPLIR response of E females, compared with their controls, were also observed. In addition, delayed or deficient habituation to restraint stress was observed in the beta-EPLIR response of E males and the ACTH response of E females. These data demonstrate that fetal E-exposed males and females both exhibit hormonal hyperresponsiveness and/or deficits in recovery after repeated exposures to restraint stress, but that the patterns of response may differ depending on the number and duration of restraint exposures, the time course measured, and whether the endpoint measured is corticosterone, ACTH, or beta-EPLIR. In addition, the finding that E and pair-fed animals both differed from their respective controls in certain developmental and hormonal measures suggests that prenatal nutritional factors may play a role in mediating some of the changes that are observed.

beta-Endorphin and blood pressure in multiple trauma victims

In addition to pain and stress, endogenous opiates and in particular beta-endorphin could be involved in the modulation of cardiovascular parameters. Several studies have thus shown increases in plasma beta-endorphin levels in the course of septic or hypovolemic shock. Our study involving 44 multiple trauma patients indicates that even in the absence of any hemodynamic disorders, there is a correlation between systolic blood pressure and plasma beta-endorphins. These results argue in favor of the existence of feedback between systolic blood pressure and plasma beta-endorphins.

Beta-endorphin in multiple trauma victims

BACKGROUND

In animals and in humans, stress is known to be accompanied by increased beta-endorphin secretion.

METHODS

Blood samples from 47 patients in a state of stress induced by multiple trauma were assessed for beta-endorphin concentration by radioimmunoassays.

RESULTS

We show that there is a clearcut correlation (Spearman's R = 0.72, P = 2.1 x 10(-6) between the level of consciousness evaluated with the Glasgow score and levels of circulating beta-endorphin. In addition, beta-endorphin levels are higher than normal in patients with Glasgow coma with scores higher than seven, and lower than normal in those with Glasgow coma scores of seven or less. Finally, in the complete absence of stress (shown by the lack of brain activity in six irreversible coma patients), there is a severe drop in the level of circulating beta-endorphin.

CONCLUSION

beta-endorphin serum levels correlate with the state of consciousness of multiple trauma patients.

Differences between alcohol-preferring (AA) and alcohol-avoiding (ANA) rats in the prodynorphin and proenkephalin systems

The motivation to drink alcohol and the eventual risk of becoming addicted are in part genetically determined. Because opioid peptides are considered central to motivated behaviors, we have analyzed opioid peptides in relevant areas of the brain of two outbred lines of rats: the alcohol-preferring [Alko Alcohol (AA)] line who voluntarily drink alcohol and the alcohol-avoiding [Alko Non-Alcohol (ANA)] line with negligible intake. (Met)enkephalinArg6Phe7 (MEAP) was measured as a marker of proenkephalin, and dynorphin A, dynorphin B, and (Leu)enkephalinArg6 as markers of the prodynorphin system. The major line differences and effects of alcohol intake were observed in mesolimbic brain areas. The mesolimbic dopamine pathway, which projects from the ventral tegmental area (VTA) to the nucleus accumbens, is central in the reward system. Basal levels of MEAP and dynorphin peptides were low in the nucleus accumbens of AA rats, whereas (Leu)enkephalinArg6 levels were lower in the VTA of these rats. Alcohol drinking caused MEAP levels in the accumbens to rise, but had no effect on prodynorphin peptides. Opioids also influence the nigrostriatal dopamine pathway. However, this study showed no significant differences for any peptide between rat lines, or effect of alcohol intake, in either substantia nigra or striatum, except for a decrease of nigral and striatal (Leu)enkephalinArg6 levels in alcohol-drinking AA rats. Large line differences were observed in the pituitary gland. AA rats had high basal levels of MEAP, which became even higher after voluntary alcohol consumption for 4 weeks, and low levels of dynorphin peptides, not affected by alcohol drinking.(ABSTRACT TRUNCATED AT 250 WORDS)

Melatonin counteracts pinealectomy-dependent decreases in rat brain [3H]flunitrazepam binding through an opioid mechanism

The effect of intracerebroventricular (i.c.v.) injection of melatonin and/or beta-endorphin on the [3H]flunitrazepam binding sites in the cerebral cortex of pinealectomized or superior cervical ganglionectomized rats was studied. Pinealectomy decreased the maximum concentration of benzodiazepine receptors (Bmax) without affecting the dissociation constant (KD), while melatonin, ineffective in control animals, counteracted the effect of pinealectomy. Intracerebroventricular injection of beta-endorphin increases Bmax in both control and pinealectomized animals, the effect being significantly higher in the latter. Simultaneous i.c.v. injection of melatonin + beta-endorphin did not further increase Bmax in any group, whereas i.c.v. injection of naloxone significantly blocked the effects of melatonin and/or beta-endorphin administration. Pineal sympathetic denervation produced a significant increase in Bmax and KD, whereas i.c.v. injection of melatonin further increased the former, restoring KD to control values. Neither i.c.v. administration of beta-endorphin or melatonin + beta-endorphin significantly modified the ganglionectomy-dependent increase in Bmax, although both treatments restored KD to control values. Naloxone administration had no effect on beta-endorphin- and melatonin + beta-endorphin-treated ganglionectomized groups, but counteracted the increased effect of melatonin on Bmax in ganglionectomized animals.

Endogenous opioid system during inspiratory loading in patients with type I diabetes

To investigate the activity of the endogenous opioid system in patients with insulin-dependent diabetes mellitus during ventilatory stress situations, we measured plasma beta-endorphin levels in six male and five female diabetic patients breathing against fatiguing inspiratory resistive loads. The patients had to generate with each inspiration an esophageal pressure (Pes) 80% of maximum until they were exhausted and could no longer develop target Pes. The loaded breathing run was repeated three times with a 1-min interval between each run. Duty cycle, tidal volume, and breathing frequency were constant in all tasks. For each run plasma beta-endorphin levels were measured, inspiratory effort sensation assessed using a modified Borg scale, and inspiratory muscle endurance evaluated by the length of time the task could be maintained (Tlim). A group of 11 sex-, age-, height-, and weight-matched healthy individuals served as control subjects. Tlim was significantly lower in the diabetic patients. Evaluating respiratory effort during the three test runs in control subjects at a time corresponding to the break point of loaded breathing in patients showed significantly lower Borg ratings in the control group than in the patient group. Baseline plasma beta-endorphin was significantly lower in the diabetic patients (10.6 +/- 2.1 versus 27.0 +/- 4.2 pg/ml, p < 0.01). Additionally, whereas resistive loaded breathing caused a further increase in plasma beta-endorphin concentration in the control group (p < 0.005), absolutely no increase was found in the diabetic patients. We conclude that the endogenous opioid system in insulin-dependent diabetic patients does not respond to stress caused by breathing against fatiguing inspiratory resistive loads.

Topography of short portal vessels in the rat pituitary gland: a scanning electron-microscopic and morphometric study of corrosion cast replicas

We applied scanning electron microscopy combined with imaging and morphometric techniques to analyze the dorsal topography and morphology of short portal vessels linking the capillary beds of the pituitary neural and anterior lobes in adult male albino rats. The pituitary microvasculature was replicated by intracarotid injection of Batson's No. 17 compound producing plastic casts that were advantageous for comprehensive morphometric analyses using an imaging device. The analysis revealed the existence of two types of portal vessels having quantitatively different morphological properties. The bilateral venular plexus of 3-4 vessels located at the base of the infundibular stalk (each venule measuring 300 microns in length and 32 microns in diameter) appears to be the major part of the short portal system in the dorsum of the rat pituitary gland. Narrower capillary-like shunt vessels (6.8 microns in diameter), of about the same length as the venules, were situated throughout other subregions of the intermediate lobe cleft. The short portal vessels of both types made direct anastomoses with the capillary networks in the neural and anterior lobes. The neural lobe capillaries were twice as numerous (1324 per mm2), and only half as wide (6.2 microns), as the sinusoidal capillaries in the anterior lobe (density of 637 per mm2; diameter of 13.7 microns). The topographical position of the portal venular system suggests that the caudolateral subregions of the pituitary neural and anterior lobes have a functional relationship dependent on rapid interlobe transfer of neurohumoral factors such as hormones via the portal blood. This process appears to be supplemented throughout the rest of the cleft between the two lobes by a small number of capillary shunts that supply the epithelial cell lobules of the intermediate lobe in situ. The findings collectively indicate that this portal system provides a constant stream of neurohumoral information that is shared moment-by-moment between the pituitary neural and anterior lobes.

Osmotic stimuli attenuate vasoactive intestinal peptide gene expression in the rat anterior pituitary gland

Studies on vasoactive intestinal peptide (VIP) in the anterior pituitary gland have shown that it is synthesized locally, physiologically regulated, and may act as a paracrine/autocrine factor. We have now investigated the regulation of anterior pituitary VIP gene expression in rats during osmotic stimulation. Both salt-loading and dehydration resulted in a progressive and marked reduction in VIP mRNA levels as determined by Northern analysis, to 10% of control levels at 14 days of salt-loading. The 1.7 and 1.0 kb VIP RNA transcripts were equally affected. Since anterior pituitary VIP is partially localized in lactotrophs we also measured prolactin (PRL) mRNA levels. In contrast to VIP, PRL mRNA levels were increased during both osmotic paradigms, the mRNA levels being significantly raised after 5 days of salt-loading to 130% of controls. Further experiments, conducted to examine the mechanism by which VIP gene expression is down-regulated during osmotic stimulation, demonstrated that dopamine and angiotensin II do not appear to be involved. The results show dissociated regulation of VIP and PRL during osmotic stimulation and provide suggestive evidence of a role for anterior pituitary VIP in the animal's osmoregulatory responses. VIP may therefore be a paracrine factor with diverse functional roles.

Regulation of vasopressin gene expression: changes in the level, but not the size, of vasopressin mRNA following endocrine manipulations

1. Regulatory interactions between the hypothalamoneurohypophyseal vasopressin (VP) axis and the endocrine systems of the anterior pituitary have been investigated in the rat by observing changes in VP mRNA expression following endocrine manipulations. 2. An increase in the level, but not size, of VP mRNA was found in the supraoptic (SON) and paraventricular nuclei (PVN) of the hypothalamus and in the neurointermediate lobe (NIL) of the pituitary following hypothyroidism (induced by drinking 6-n-propyl-2-thiouracil; PTU) and adrenalectomy. Hypothyroidism induced by alternative procedures (surgical thyroidectomy or PTU injections) did not exert similar effects. 3. Treatment with the dopamine agonist bromocriptine to reduce prolactin secretion raised levels of VP mRNA in the NIL only. Castration did not up-regulate VP mRNA levels. 4. Since the observed effects on VP mRNA levels occur in the absence of changes in plasma osmolality, these results provide evidence of nonosmotic regulation of VP gene expression, an effect which is observed most clearly in the NIL pool of VP mRNA. Furthermore, the effects are distinct from changes in VP mRNA levels associated with raised plasma osmolality since the VP mRNA size was not increased.

Hyperthermia and endorphins

This paper discusses the role of endogenous opioids in response to hyperthermia and the alterations observed in drug or alcohol addicts. Endorphins, rather than enkephalins are involved in adaptation to heat in the central nervous system. The pituitary secretion of beta endorphin together with ACTH in response to thermal stress provided the opportunity to measure the opioid reactivity to hyperthermia in health and toxicomania, as an index of opioid function, in adaptation to heat. The review of the data in the literature shows absent responses of beta endorphin and its related hormone ACTH to the thermal stress of sauna in heroin, cocaine or alcohol addicts. A common explanation for this phenomenon is that the long-term stimulation of hypothalamic opioid neurotransmission that is produced directly or indirectly by heroin, alcohol or cocaine, disrupts the opioid response to thermal stress, and thus the adaptation to heat.

Enkephalins, brain and immunity: modulation of immune responses by methionine-enkephalin injected into the cerebral cavity

There is a large number of interactions at molecular and cellular levels between the nervous system and the immune system. It has been demonstrated that the opioid neuropentapeptide methionine-enkephalin (Met-Enk) is involved in humoral and cell-mediated immune reactions. Met-Enk injected peripherally produces a dual and dose-dependent immunomodulatory effect: high doses suppress, whereas low doses potentiate the immune reactivity. The present mini-review concerns the immunological activity of Met-Enk after its administration into the lateral ventricles of the rat brain, and describes the extraordinary capacity of centrally applied Met-Enk to regulate/modulate the immune function. This survey is composed of sections dealing with (a) the role of opioid peptides in the central nervous system (CNS); (b) the activity of opioid peptides in the immune system; (c) the application of Met-Enk into the cerebral cavity; (d) the influence of centrally administered Met-Enk on nonspecific local inflammatory reaction; (e) the effect of Met-Enk injected intracerebroventricularly (i.c.v.) on specific delayed hypersensitivity skin reaction, experimental allergic encephalomyelitis, anaphylactic shock, plaque-forming cell response, and hemagglutinin production; (f) the central antagonizing action of quaternary naltrexone, an opioid antagonist that does not cross the brain-blood barrier, on Met-Enk-induced immunomodulation; (g) the alteration of immune responsiveness by i.c.v. injection of enkephalinase-degrading enzymes; (h) the participation of the brain-blood/blood-brain barrier in the CNS-immune system interaction; and (i) the role of opioid receptors in immunological activity of Met-Enk. A hypothesis has been advanced for the reaction of Met-Enk and opioid receptor sitting on the cell membrane. This concept suggests that the constellation of chemical residues of enkephalin and receptor in the microenvironment determines the binding between the opioid partners. The plurality of conformational structures of enkephalins and receptors makes possible their involvement in a variety of processes which occur in different physiological systems, including the nervous system and the immune system, and intercommunications between the two systems.

A brain-warming function for REM sleep

During REM sleep, arterial blood flow, neuronal firing rates, metabolism, and temperature increase in many parts of the CNS. Eye muscle tone also increases, and the eyes exhibit bursts of rapid movements. If one of the functions of sleep is to conserve energy, then it is curious that energy is so conspicuously expended in the vicinity of the CNS during REM sleep. The author hypothesizes that homeotherms use REM sleep to produce heat in order to maintain a high, stable temperature in a restricted CNS core during sleep. The fact that several of the active features of REM sleep heat the CNS, and the fact that REM sleep propensity increases when core temperature physiologically decreases, seem consistent with the hypothesis that REM sleep is a regulated mechanism for warming the CNS.

Modulation of pituitary gonadotropins and prolactin secretion by testosterone in vitro

Investigations were undertaken to study the differential modulation of LH, FSH and PRL secretion by testosterone (T) using whole pituitary (PI) or pituitary-hypothalamus coincubates (PHC) as in vitro constructs. PI and PHC from intact and castrated rats were incubated with or without T thrice, for 24 h each, (24 h x 3, total incubation period 72 h). The spent media was replenished every 24 h. At the end of 72 h, a few of the pituitary glands were challenged with 10 nM LHRH for 4 h. The spent media and pituitary glands were analyzed for LH, FSH and PRL using specific RIAs. Incubation of PI or PHC from intact rats with T stimulated the release of LH and FSH but inhibited the release of PRL. T had no effect on the intrapituitary contents of LH but inhibited intrapituitary contents of FSH and PRL, as compared to controls incubated without T. Castration increased intrapituitary contents of LH and FSH with concomitant decrease in PRL levels. Incubation of PI or PHC from castrated rats with T inhibited intrapituitary contents of LH to intact pituitary levels, while PRL levels were further reduced instead of being ameliorated. It is concluded that PI or PHC can be used as convenient in vitro models to monitor the effect of castration or of T modulation of pituitary and hypothalamus functions. T does not affect the synthesis of LH at the gonadotroph level but facilitates the regulation of intracellular LH and FSH levels. It is postulated that T inhibits the synthesis of FSH/PRL at the gonadotroph/lactotroph levels.

Differences in the brain and pituitary beta-endorphin system between the alcohol-preferring AA and alcohol-avoiding ANA rats

The content of pro-opiomelanocortin (POMC) mRNA was determined in the hypothalamus, as well as in the anterior and intermediate lobes of the pituitary gland of the alcohol-preferring AA and alcohol-avoiding ANA rats under basal conditions. In addition the content of beta-endorphin-like immunoreactivity (beta-EPLIR) was measured in nine brain regions, the anterior and intermediate lobes of the pituitary gland and the serum. The content of beta-EPLIR was significantly higher in the septum and significantly lower in the amygdala, and periaqueductal gray matter of the AA rats, while there was no significant difference between the AA and ANA rats in the arcuate nucleus plus median eminence, nucleus accumbens, caudate, hippocampus, and cortex. HPLC analysis indicated no significant differences in the relative proportions of non-acetyl and acetyl forms of beta-endorphin peptides in the hypothalamus, distinct brain regions, and anterior and neurointermediate lobes of the pituitary gland, between the AA and ANA rats. The content of POMC mRNA but not of beta-EPLIR was significantly higher in the hypothalamus and neurointermediate lobe of the AA rats, while the content of both beta-EPLIR and POMC mRNA were significantly higher in the anterior pituitary of the AA than of the ANA rats. Thus, there are genetically determined differences in the pituitary and brain beta-endorphin system between the AA and ANA rats, which may be important in controlling the differences in the voluntary ethanol consumption exhibited by these animals.

Pituitary follicular cells secrete an inhibitor of aortic endothelial cell growth: identification as leukemia inhibitory factor

Medium conditioned by bovine pituitary follicular cells paradoxically inhibits the growth of adult bovine aortic endothelial (ABAE) cells at dilutions that are instead mitogenic to adrenal cortex capillary endothelial (ACCE) cells, suggesting that follicular cells secrete a growth inhibitor with a selectivity for ABAE cells. The ABAE cell inhibitory activity was purified to apparent homogeneity by a combination of size-exclusion chromatography, ion-exchange chromatography, and two reversed-phase steps on a C4 column. Microsequencing of the purified material revealed a single NH2-terminal amino acid sequence, identical to that of leukemia inhibitory factor (LIF), a glycoprotein originally identified by its ability to inhibit the growth of MT1 mouse leukemia cells and subsequently found to have numerous effects. Recombinant human LIF inhibited the growth of ABAE cells as effectively as transforming growth factor beta (TGF beta 1). However, it failed to inhibit markedly the growth of ACCE cells, whereas TGF beta 1 dramatically inhibited their growth. Recombinant human LIF also failed to induce a significant angiogenic response in the chicken chorioallantoic membrane, indicating that, unlike TGF beta, LIF probably does not induce the release of direct-acting angiogenic factors from inflammatory cells. The presence of LIF in follicular cells may relate to the peculiar vascular organization of the pituitary gland, where no arteries reach the pars distalis and all of the blood supply to this area is by capillaries.

Effect of reserpine on the inhibition of prolactin released from different pituitary constructs in vitro by dopamine, bromocriptine and apomorphine

Hourly release of Prolactin by pituitary constructs 1 whole pituitary (PI), adenohypophysis (P-N) and pituitary-hypothalamus co-incubate (PHC) were compared. Adenohypophysis secreted significantly more prolactin than PI and PHC, while PHC secreted significantly less than PI. Co-incubation of (P-N) with posterior pituitary reduced the elevated secretion of prolactin. Addition of dopamine (10(-7) M), bromocriptine (10(-7) M) and apomorphine (5 x 10(-8) M) to these constructs did not affect the release of prolactin from PI but inhibited the same from (P-N) and PHC. Treatment with reserpine increased serum prolactin levels but intrapituitary prolactin contents were decreased. Hourly release of prolactin from pituitary constructs derived from reserpine-treated rats was significantly reduced as compared to ascorbic acid--treated controls. Inclusion of dopamine (10(-7) M), bromocriptine (10(-7) M) and apomorphine (5 x 10(-8) M) in these constructs inhibited prolactin secretion further. In vitro addition of perphenazine stimulated the release of prolactin by PHC but was without any effect on PI and (P-N). The data are interpreted to suggest that dopamine in posterior pituitary may be an important determinant of hypothalamic modulation of prolactin secretion.

The vascular endothelial growth factor family of polypeptides

Vascular endothelial growth factor (VEGF) was identified as a heparin-binding polypeptide mitogen with a target cell specificity restricted to vascular endothelial cells. Molecular cloning reveals the existence of four species of VEGF having 121, 165, 189, and 206 amino acids. These have strikingly different secretion patterns, which suggests multiple physiological roles for this family of polypeptides. The two shorter forms are efficiently secreted, while the longer ones are mostly cell-associated. Alternative splicing of mRNA, rather that transcription from different genes, is the mechanism for their generation. In situ hybridization reveals that the VEGF mRNA is widely distributed in most tissues and organs and expressed at particularly high levels in areas of active vascular proliferation, like the ovarian corpus luteum. Ligand autoradiography on rat tissue sections demonstrates that VEGF binding sites are associated with vascular endothelial cells of both fenestrated and non-fenestrated capillaries and with the endothelium of large vessels, while no displaceable binding is evident on non-endothelial cell types. These findings support the hypothesis that VEGF plays a highly specific role in the maintenance and in the induction of growth of vascular endothelial cells.

Arginine vasopressin in Cushing's disease

Bilateral simultaneous blood samples were taken from the inferior petrosal sinuses of nine patients with Cushing's disease for measurement of adrenocorticotropin (ACTH), vasopressin (AVP), prolactin, growth hormone, luteinising hormone (LH), and follicle stimulating hormone (FSH). Inter-sinus gradients for ACTH (range 3.3-18.2) and AVP (2.0-375) correctly lateralised the microadenoma in seven of these patients. One additional patient showed an increased gradient for AVP but not ACTH on the side of the tumour. The correlation between the AVP and ACTH concentrations in the petrosal sinus draining the microadenoma was significant. Petrosal sinus plasma concentrations of prolactin and growth hormone were also significantly higher on the side of the tumour than on the non-tumour side. Evidence against a non-specific tumour effect on the secretion of all pituitary hormones was the fact that in most cases the gradients for LH and FSH were not significant. It is proposed that increased delivery of AVP to part of the pituitary may result from an aberrant blood supply, and that AVP may interact with corticotropin releasing factor to promote tumour growth and ACTH release.

Effects of glipizide on beta-endorphin secretions in response to hyperglycaemia in obese cafeteria rats

Regulation of blood glucose involves the integration of the central nervous system with both hormonal and neural mechanisms. Considerable evidence suggests that beta-endorphin is involved in the regulation of feeding in experimental animals and man. Previous studies have shown that beta-endorphin plays an important role during hyperglycaemia. Glipizide has been shown to increase glucose metabolism by both pancreatic and extrapancreatic actions. This study indicates that glipizide may exert its pharmacological action in obese cafeteria rats through a modification of beta-endorphin secretions via central and peripheral mechanisms.

Microanatomy and possible clinical significance of anastomoses among hypothalamic arteries

We examined anastomoses among the hypothalamic arteries in 14 human brains using an injection technique, microdissection, and a stereoscopic microscope. Five to 22 anastomoses (mean 10.1) were found in all 14 brains on each side, varying from 20 to 280 (mean 71) microns in diameter and from 0.1 to 5.3 (mean 1.52) mm long. A single hypothalamic artery may be connected to other vessels by one to 10 anastomoses. The anastomoses were channel-like or plexiform; both types may be ipsilateral or right-left. They connected the hypothalamic arteries "end-to-end," "end-to-side," and "side-to-side." The interconnected arteries ranged from 30 to 1,900 (mean 148) microns in diameter. Anastomoses were most frequent among the commissural arteries and in the distribution of the superior hypophyseal arteries and the tuberoinfundibular branches of the posterior communicating artery. The largest anastomoses were found among the tuberoinfundibular branches of the posterior communicating and internal carotid arteries, as well as among the premamillary arteries and the mamillary branches. We discuss the neurologic, neuroendocrinologic, and neurosurgical significance of the described anastomoses.

Effects of glipizide on beta-endorphin concentration in the brain of genetically diabetic (db/db) mice

Sulphonylurea drugs have been shown to augment glucose metabolism by both pancreatic and extrapancreatic actions. The regulation of glucose involves a modification of beta-endorphin secretions via central and peripheral mechanisms. beta-Endorphin participates in the regulation of feeding and is implicated both in obesity and diabetes mellitus. This study shows that glipizide could exert its pharmacological action in genetically diabetic (db/db) mice via beta-endorphin secretions by a central mechanism.

Light microscopic study of the hypophyseal angioarchitecture in the rabbit

This study describes the hypophyseal angioarchitecture found in 79 adult New Zealand white rabbits. The pituitary glands and attached hypothalami were removed and carefully processed following routine histological methods, and the vascular organization was studied by light microscopy. Whole mounts of the pituitary median eminence complex were prepared and studied with a binocular dissecting microscope employing transmitted and epi-illumination. Arterial blood was found to be directed primarily to the neurohypophysis by the superior hypophyseal artery (SHA) and the inferior hypophyseal artery (IHA). A direct arterial blood supply was found to the adenohypophysis, but was limited solely to the pars intermedia by branches of the anterior hypophyseal artery (AHA) and the IHA. Capillaries of the pars intermedia were subdivided into an intermediate and a superficial plexus. The superficial plexus was situated between the intermediate plexus and the capillaries of the infundibular process. Capillaries of the superficial plexus did not form anastomoses between themselves, but ramified into the intermediate plexus to form a dense network of anastomosing capillaries that were continuous with capillaries of the pars distalis. A direct arterial blood supply was found only to the superficial plexus.