Randomized pilot study of cabergoline, a dopamine receptor agonist: effects on body weight and glucose tolerance in obese adults.

AIM: Dopaminergic hypofunction and hyperprolactinaemia have been implicated in the pathogenesis of obesity and glucose intolerance. The aim of this pilot study was to determine the efficacy of cabergoline, a dopamine receptor agonist, on body weight and glucose tolerance in obese non-diabetic persons with normal plasma prolactin levels. METHODS: This 16-week double blind, placebo-controlled pilot study randomized non-diabetic obese adults (body mass index 30-42 kg/m(2) ) to placebo or cabergoline (0.25 mg twice weekly for 4 weeks followed by 0.5 mg twice weekly for the next 12 weeks). Of 40 subjects enrolled, 29 completed 16 weeks: 16 randomized to placebo and 13 to cabergoline. All subjects were counselled on a 500 kcal/day calorie deficit diet. A 75-g oral glucose tolerance test was performed at baseline and at 16 weeks. RESULTS: As expected, prolactin levels decreased after cabergoline (p < 0.001). Weight loss was similar after placebo compared with cabergoline treatment: 1.0 vs. 1.2% body weight, respectively. Fasting glucose levels did not differ between groups after treatment, however, 90-min postprandial glucose and insulin decreased in the cabergoline group only (p = 0.029). HOMA-IR (homeostasis model of assessment) increased by 40% after placebo and 1.5% after cabergoline treatment. CONCLUSIONS: This pilot study suggests that cabergoline therapy may improve glucose tolerance independent of weight loss, however, a larger, longer term study of dopamine receptor agonist therapy in obese individuals is warranted to confirm this finding.

Hypothalamic-pituitary sarcoidosis.

Patients with sarcoidosis may develop hypopituitarism secondary to granulomatous infiltration of the pituitary and hypothalamus. All degrees of anterior pituitary insufficiency can occur, ranging from selective deficiency to panhypopituitarism; diabetes insipidus occurs frequently. Commonly associated neurologic manifestations are cranial neuropathies, aseptic meningitis, and visual field defects. Although neurologic deficits respond well to corticosteroids, hormonal abnormalities generally persist despite therapy.

Spectrum of Adrenal Dysfunction in Patients with Acquired Immunodeficiency Syndrome Evaluation of Adrenal and Pituitary Reserve with ACTH and Corticotropin-Releasing Hormone Testing.

Patients with acquired immunodeficiency syndrome (AIDS) have been reported to develop abnormalities of the endocrine system and in particular of the hypothalamic-pituitary-adrenal (HPA) axis. To define the abnormalities of HPA function in AIDS patients better, we performed ACTH and ovine corticotropin-releasing hormone (oCRH) testing in a group of AIDS patients and oCRH testing in a group of healthy subjects. Our study found that in AIDS patients with normal ACTH testing, oCRH testing revealed a variety of subclinical abnormalities of ACTH and cortisol responses. Although we did not find frank adrenal insufficiency in any of these AIDS patients, it remains to be determined if any of the subclinical abnormalities we identified are predictive of clinically significant adrenal insufficiency; it may be that as AIDS patients live longer, the subclinical abnormalities will progress to adrenal insufficiency. (Trends Endocrinol Metab 1997;8:173-180). (c) 1997, Elsevier Science Inc.

Regulation of beta-endorphin, corticotropin-like intermediate lobe peptide, and alpha-melanotropin-stimulating hormone in the hypothalamus by testosterone.

Ovarian steroids have previously been shown to regulate the hypothalamic content of beta-endorphin (beta EP) and its release into hypophyseal portal blood. Although the hypothalamic content of beta EP in cycling female rats was unchanged by ovariectomy, chronic treatment of ovariectomized rats with estradiol lowered hypothalamic beta EP levels. In this study, the hypothalamic content of beta EP was compared in male and cycling female rats, and the effects of orchiectomy and testosterone replacement on hypothalamic beta EP were examined. The beta EP content of the medial basal hypothalamus (MBH) was significantly higher in female rats compared to that in males of either the same weight (175-200 g) or the same age (65 days; P less than 0.025). When male rats were studied 4 weeks after castration, the beta-EP content of the MBH increased from a value of 2100 +/- 103 fmol in the controls to 2680 +/- 126 fmol (P less than 0.005). The hypothalamic beta EP content in the castrated males was similar to that in the intact females (2700 +/- 158 fmol). The increase in hypothalamic beta EP induced by castration was blocked by testosterone replacement. When orchiectomized animals were treated for 4 weeks with Silastic capsules filled with testosterone, there was a significant fall in the hypothalamic content of beta EP compared to that in the unreplaced animals. beta EP fell from 3180 +/- 115 to 2033 +/- 53 fmol in the MBH (P less than 0.001), from 1693 +/- 122 to 934 +/- 80 fmol in the anterior hypothalamus (P less than 0.001), and from 148 +/- 26 to 90.3 +/- 11 fmol in the median eminence (P less than 0.05). Testosterone replacement was also associated with a significant decline in the hypothalamic content of corticotropin-like intermediate lobe peptide and alpha MSH. Corticotropin-like intermediate lobe peptide fell from 2400 +/- 53 to 1560 +/- 84 fmol in the MBH (P less than 0.001) and from 1200 +/- 74 to 805 +/- 94 fmol in the anterior hypothalamus (P less than 0.01). alpha MSH fell from 1660 +/- 162 to 884 +/- 75 fmol in the MBH (P less than 0.001) and from 823 +/- 106 to 544 +/- 92 fmol in the anterior hypothalamus (P less than 0.05). Thus, testosterone, as well as estradiol, affects the hypothalamic content of several proopiomelanocortin-derived peptides. The effect on brain peptide content, however, depends on whether the steroids are secreted relatively constantly, as in the male, or fluctuate, as in the cycling female.

Interaction between beta-endorphin and alpha-melanocyte-stimulating hormone in the control of prolactin and luteinizing hormone secretion in the primate.

The ability of alpha MSH, a POMC-derived peptide, to antagonize the effects of beta-endorphin (beta EP) on PRL and LH secretion was studied in the primate. Seven ovariectomized rhesus monkeys bearing chronic indwelling third ventricular catheters for peptide infusion were used for these studies. Peripheral blood samples for PRL and LH RIA were obtained every 15 min during a 3-h control period when saline was infused into the ventricle, followed by a 5-h period of peptide infusion at a rate of 25 microliters/h. When beta EP was infused at a dose of 5 micrograms/h, plasma PRL rose from a mean baseline of 3.5 +/- 0.7 ng/ml to a peak of 21.3 +/- 2.2 ng/ml. When the same animals were infused with 20 micrograms alpha MSH together with 5 micrograms beta EP, the peak concentration of PRL was reduced to 8.2 +/- 1.7 ng/ml (P less than 0.001). When a higher dose of beta EP (20 micrograms/h) was infused, PRL rose to a peak of 38.2 +/- 1.8 ng/ml. This response was again markedly blunted, and the peak PRL response was reduced to 7.3 +/- 2.2 ng/ml when 20 micrograms beta EP were infused together with 80 micrograms alpha MSH (P less than 0.001). Analysis of the area under the plasma PRL concentration curves demonstrated a significant reduction in area during the 5-h infusion with beta EP plus alpha MSH compared to that during infusion of beta EP alone. The mean area was reduced from 3480 +/- 570 ng min/ml after 5 micrograms beta EP alone to 1030 +/- 200 after 5 micrograms beta EP plus 20 micrograms alpha MSH and from 6230 +/- 990 after 20 micrograms beta EP to 1020 +/- 320 ng min/ml after 20 micrograms beta EP plus 80 micrograms alpha MSH (P less than 0.01). Des-acetyl alpha MSH (80 micrograms) was also effective in reducing the PRL response to 830 +/- 380 ng min/ml (P less than 0.05). The suppression of pulsatile LH release by beta EP was also attenuated by alpha MSH. During the 5-h infusion of beta EP, total LH secretion was reduced to 65.9 +/- 3.8% of that measured during the 3-h saline infusion compared to 87.2 +/- 2.7% after infusion of beta EP plus alpha MSH (P less than 0.001) or 91.7 +/- 4.1% after beta EP plus des-acetyl alpha MSH (P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Brain beta-endorphin during pregnancy, parturition, and the postpartum period.

Brain beta-endorphin (beta-EP) was measured in the rat during pregnancy, parturition, and the postpartum period. beta-EP increased in the hypothalamus, midbrain, and amygdala during gestation and remained elevated through delivery until 1-2 days postpartum. The concentration of beta-EP increased in the hypothalamus from 31.8 +/- 1.4 (+/- SE) ng/mg protein in nonpregnant controls to 41.4 +/- 1.8 and 39.2 +/- 1.9 during early (8-10 days) and late (18-20 days) pregnancy, respectively, and in the midbrain from 3.20 +/- 0.17 to 5.21 +/- 0.30 and 5.25 +/- 0.64 ng/mg protein (P less than 0.01). In another experiment, the brain content of beta-EP expressed as nanograms per region, increased from 12.6 +/- 0.29 to 14.7 +/- 0.33 in the hypothalamus, from 4.09 +/- 0.44 to 6.03 +/- 0.34 in the midbrain, and from 0.93 +/- 0.11 to 1.32 +/- 0.06 ng in the amygdala at 16-17 days of gestation compared with that in nonpregnant controls (P less than 0.01). When hypothalamic beta-EP was measured 1 week postpartum in lactating and nonlactating rats, a significant decline in the beta-EP concentration of both groups was noted compared with that measured during pregnancy; beta-EP levels were similar in the lactating and nonlactating rats. We conclude that pregnancy and parturition are associated with significant changes in brain beta-EP and suggest that beta-EP of central rather than peripheral origin may mediate changes in pain perception and maternal behavior during pregnancy.

Androgen regulation of proopiomelanocortin gene expression and peptide content in the basal hypothalamus.

Previous studies have shown that the hypothalamic content of beta-endorphin (beta EP) and other POMC-derived peptides increases 4 weeks after orchiectomy and that this increase can be prevented by testosterone replacement. To determine if these changes in hypothalamic beta EP content are secondary to changes in the biosynthesis of beta EP we have measured POMC mRNA levels in intact and castrated adult male rats with and without testosterone replacement. After either 2 or 4 weeks of treatment the medial basal hypothalamus (MBH) was collected and homogenized. An aliquot was removed for beta EP RIA, RNA was isolated, and the amount of POMC mRNA was measured using a solution hybridization S1 nuclease protection assay. In agreement with previous results, the content of beta EP in the MBH from 4-week castrated animals (7930 +/- 568 pg/mg protein) was significantly increased compared to that in either castrated and testosterone-replaced rats (5792 +/- 568 pg/mg; P less than 0.02) or intact controls (6027 +/- 349 pg/mg; P less than 0.02). POMC mRNA in the MBH from the 4-week castrated group was significantly higher compared to that in the castrated and testosterone-replaced group (2.61 +/- 0.33 vs. 1.7 +/- 0.22 pg/microgram RNA; P less than 0.05), which is parallel to the changes we found in beta EP peptide levels. Two weeks after castration no significant change was detected in the beta EP content in the MBH from castrated rats (5401 +/- 318 pg/mg protein) compared to that in the castrated and testosterone-replaced group (4848 +/- 304 pg/mg protein). However, we were able to detect a significant difference in the amount of POMC mRNA in the 2-week castrated group (1.47 +/- 0.267 pg/microgram RNA) compared to that in the 2-week castrated and testosterone-replaced group (0.815 +/- 0.061 pg/microgram RNA; P less than 0.05). The finding that testosterone replacement for either 2 or 4 weeks to castrated rats significantly reduced POMC mRNA levels suggests that sex steroids have an inhibitory effect on the biosynthesis of POMC in the MBH.

Characterization of plasma beta-endorphin immunoactivity in the fetal lamb: effects of gestational age and hypoxia.

To characterize the immunological forms of beta-endorphin (beta-EP) in the fetal circulation, total beta-EP immunoactivity [beta-EPi] and N-acetyl beta-EPi were measured in the plasma of chronically catheterized fetal lambs in undisturbed conditions and before, during, and after periods of controlled hypoxia. Measurements of the peptide concentrations in each plasma sample were made by RIA using an antiserum to the midportion of beta-endorphin which cross-reacts with both acetylated and unacetylated forms of the peptide as well as with beta-lipotropin, and a second antiserum which reacts only with acetylated forms of beta-EP. In 25 plasma samples from 12 fetal animals at 113-142 days gestation, total beta-EPi was 87.0 +/- 10.9 pg/ml, while N-acetyl beta-EPi was 90.8 +/- 7.7 pg/ml (mean +/- SE). When a plasma pool obtained from 3 fetuses in the basal state was extracted and chromatographed on Sephadex G-50, most of the N-acetyl beta-EPi eluted in the same position as the synthetic N-acetyl beta-EP standard. Thus, most of the beta-EPi in the plasma of the unstressed fetus could be accounted for by N-acetylated forms of the peptide. These are the major forms of beta-EP produced by the intermediate lobe of the pituitary. To examine the effects of acute hypoxia on fetal plasma peptide levels, pregnant ewes were exposed to 10% O2 in N2 for 30 min. In 15 studies at 113-142 days gestation, mean fetal PO2 decreased from 21.7 +/- 0.6 to 11.0 +/- 0.7 mm Hg (P less than 0.001). Total beta-EPi increased significantly from 93.0 +/- 17.7 to 527 +/- 146 pg/ml during hypoxia and returned toward basal values after 30 min of recovery to 372 +/- 116 pg/ml (P less than 0.02). Over the same intervals, N-acetyl beta-EPi did not change significantly, with mean levels of 88.5 +/- 10.7, 123 +/- 16.3, and 130 +/- 16.8 pg/ml. This shows that the increase in total beta-EPi with hypoxia could not be accounted for by an increase in N-acetyl beta-EPi. Our finding that most of the total beta-EPi in the circulation of the undisturbed fetus is N-acetyl beta-EPi favors an intermediate lobe origin. Since beta-EP is inactivated by N-acetylation, these data suggest that this immunoactivity has little or no biological activity. Enhanced release of total beta-EPi during hypoxia, which could not be accounted for by acetylated forms, suggests that this type of stress activates the anterior pituitary lobe and results in increased plasma concentrations of the biologically active peptide.

Antagonism of beta-endorphin-induced prolactin release by alpha-melanocyte-stimulating hormone and corticotropin-like intermediate lobe peptide.

The ability of two proopiomelanocortin-derived peptides, alpha MSH and corticotropin-like intermediate lobe peptide (CLIP) [ACTH (18-39)] to antagonize the stimulation of PRL secretion by beta-endorphin (beta EP) was studied in the rat. When 50 ng beta EP were injected into the lateral cerebral ventricle, plasma PRL rose from a mean baseline of 1.87 +/- 0.43 ng/ml (+/- SEM) to a peak of 23.0 +/- 3.67 ng/ml 10 min after the injection. When the same animals received 500 ng alpha MSH together with 50 ng beta EP, the peak concentration of PRL was reduced by 74% to 6.05 +/- 1.43 ng/ml (P less than 0.005). After the injection of 500 ng CLIP together with 500 ng beta EP, the peak concentration of PRL was reduced by 47% to 12.8 +/- 3.09 ng/ml (P less than 0.01). Total PRL release, determined by calculating the areas under the plasma PRL concentration curves, was also significantly reduced by the injection of alpha MSH or CLIP. A dose of 100 ng alpha-MSH or CLIP also antagonized the stimulation of PRL secretion by 50 ng beta EP. PRL release was reduced by 62% after administration of 100 ng alpha MSH (P less than 0.001) and by 43% after 100 ng CLIP (P less than 0.05). When 100 ng alpha MSH and 100 ng CLIP were injected together, there was an additive effect in blocking the stimulation of PRL release by beta EP, and the peak plasma PRL concentration was reduced by 81%. Des-acetyl alpha MSH, the predominant form of alpha MSH in the hypothalamus, was also very effective in antagonizing beta EP-induced PRL release. The peak PRL concentration was reduced by 52% after administration of 100 ng des-acetyl alpha MSH plus 50 ng beta EP compared with that after beta EP alone (P less than 0.005). We conclude that relatively low doses of both alpha MSH and CLIP can effectively antagonize the actions of beta EP on pituitary PRL release. These findings suggest the possibility that differential posttranslational processing of proopiomelanocortin may serve as a regulator of anterior pituitary function.

Differential effects of estradiol on the adrenocorticotropin responses to interleukin-6 and interleukin-1 in the monkey.

Endotoxin and the inflammatory cytokines interleukin (IL)-1 and IL-6 are potent activators of the hypothalamic-pituitary-adrenal (HPA) axis. Although estradiol (E(2)) has been shown to enhance the HPA response to certain types of stress, previous studies in the rodent have shown that HPA responses to endotoxin and to IL-1 were enhanced by ovariectomy and attenuated by E(2). The mechanisms underlying these observations are unclear, but there is evidence that E(2) may have direct inhibitory effects on IL-6 synthesis and release. Because endotoxin and IL-1 both stimulate IL-6, it is possible that the E(2)-induced suppression of the HPA response to endotoxin and IL-1 results from decreased IL-6 release. We have therefore examined the ACTH response to IL-6 and IL-1beta in six ovariectomized rhesus monkeys with and without 3 weeks of E(2) replacement. In the first study, plasma ACTH levels peaked at 60 min after iv injection of 6 microg recombinant human IL-6. Both the ACTH response, over time, and the area under the ACTH response curve were significantly higher in the E(2)-treated animals (P < 0.05). The peak ACTH level was 66 +/- 16 pg/ml without E(2) vs. 161 +/- 69 pg/ml with E(2). In the second study, iv infusion of recombinant human IL-1beta (400 ng) produced plasma IL-6 levels comparable with those seen after IL-6 injection in the first study. In the IL-1 study, however, there was a significant attenuation of the ACTH response, over time, in the E(2)-treated animals (P < 0.001); the peak ACTH level was 83 +/- 34 pg/ml vs. 13 +/- 4.4 pg/ml after E(2). The IL-6 response was similarly attenuated (P < 0.001); the peak IL-6 level was 614 +/- 168 pg/ml vs. 277 +/- 53 pg/ml after E(2) treatment. Our results demonstrate that physiological levels of E(2) enhance the ACTH response to IL-6 but attenuate the ACTH response to IL-1. The attenuated ACTH response to IL-1 was accompanied by a blunted IL-6 response. Our results suggest that the blunted HPA response to IL-1 can be explained, at least in part, by E(2)-induced alterations in IL-6 release. It remains to be determined whether E(2) affects other inflammatory mediators that also participate in this process.

Alpha-melanocyte-stimulating hormone antagonizes the neuroendocrine effects of corticotropin-releasing factor and interleukin-1 alpha in the primate.

alpha-Melanocyte stimulating hormone (alpha-MSH), a peptide derived from POMC has previously been shown to antagonize the action of exogenously administered beta-endorphin (beta-EP) on pituitary PRL and LH release in the primate. In this study, we have tested the ability of alpha-MSH to block some of the acute pituitary effects of CRF and interleukin-1 alpha (IL-1 alpha), effects which are thought in part to result from the release of endogenous beta-EP. Experiments were performed in ovariectomized rhesus monkeys bearing a chronically implanted lateral ventricular cannula for peptide infusion. Peripheral blood samples for LH, cortisol, and PRL RIA were obtained at 15-min intervals during a 3-h control period when saline was infused into the ventricle, followed by a 5-h experimental period. CRF (15 micrograms/h) infused alone for 5 h caused a significant suppression of pulsatile LH release; by the fifth hour, LH secretion was reduced to 32.5 +/- 2.4% of the control saline infusion. The CRF-induced suppression of LH was prevented by coinfusion of alpha-MSH (60 micrograms/h); by the fifth hour LH was 89.0 +/- 3.6% of the control (P less than 0.05 vs. CRF alone). alpha-MSH also prevented the CRF-induced decrease in LH pulse frequency (P less than 0.05). IL-1 alpha (4.2 micrograms) was infused alone for 30 min or in combination with alpha-MSH (120 micrograms/h for 2 h). After IL-1 alpha alone, LH decreased to 30.1 +/- 2.4% of baseline at 5 h. This decrease was prevented by alpha-MSH; by 5 h LH was 101 +/- 5.1% of baseline (P less than 0.005 vs. IL-1 alpha alone). IL-1 alpha did not affect LH pulse frequency but pulse amplitude was reduced; this reduction was prevented by alpha-MSH (P less than 0.05). IL-1 alpha also stimulated PRL release. PRL rose from a mean baseline of 3.5 +/- 0.3 ng/ml to a peak of 13.8 +/- 2.7 ng/ml; after coinfusion of alpha-MSH the mean peak PRL response was only 4.4 +/- 1.5 ng/ml (P less than 0.001 vs. IL-1 alpha alone). After CRF infusion, cortisol increased to 136 +/- 7.9% of the mean morning baseline concentration. This increase was not prevented by alpha-MSH coinfusion; after CRF plus alpha-MSH, cortisol increased to 121 +/- 6.0% of baseline. In contrast, alpha-MSH prevented the IL-1 alpha-induced increase in cortisol: 167 +/- 15.5% vs. 91.7 +/- 8.3% (P less than 0.005).(ABSTRACT TRUNCATED AT 400 WORDS)

beta-Endorphin in hypophyseal portal blood: variations throughout the menstrual cycle.

Concentrations of beta-endorphin were measured in the venous effluent of the hypothalamus (hypophyseal portal blood) at various phases of the menstrual cycle and after ovariectomy in rhesus and pigtailed monkeys. In the rhesus, beta-endorphin concentrations were high during the mid- to late follicular phase [737 +/- 256 pg/ml (mean +/- SE)] and the luteal phase (1675 +/- 1108) of the menstrual cycle, but were undetectable (less than 133) at menstruation. Concentrations were also high in pigtailed monkeys during stages of the menstrual cycle other than at menstruation (4870 +/- 1090 pg/ml), but undetectable (less than 133) 4--12 months after ovariectomy. These results indicate that beta-endorphin concentrations in hypophyseal portal blood are related to menstrual cycle events, probably changes in ovarian steroids; this in turn suggests that beta-endorphin may participate in the ovarian feedback regulation of gonadotropin secretion.

Failure of beta-endorphin to stimulate prolactin release in the pituitary stalk-sectioned monkey.

To study the locus at which opioids act to release PRL in vivo, beta-endorphin (beta-EP) was injected into intact and pituitary stalk-sectioned monkeys. In each of five intact monkeys, serum PRL rose to peak concentrations of 200-300% of baseline 20 min after injection. In contrast, beta-EP failed to cause any PRL increase in four stalk-sectioned animals. Beta-EP also failed to stimulate PRL in two stalk-sectioned monkeys receiving estrogen replacement, indicating that estrogen deficiency was not the cause of their failure to respond. To test possible antagonism of dopamine by beta-EP directly at the pituitary, L-dopa was given to six stalk-sectioned monkeys with and without beta-EP pretreatment. No alteration of the PRL suppression by L-dopa was observed Disappearance of injected beta-EP from plasma was studied in four intact monkeys. Initial and terminal half-lives ranged from 2.3-4.0 min and from 16.0-30.2 min, respectively; MCRs ranged from 70-170 ml/min. We conclude that beta-EP does not stimulate PRL secretion either directly or by interacting with dopamine at the pituitary level. These results support a hypothalamic rather than a direct pituitary site of action for opioid-stimulated PRL release.

High levels of beta-endorphin in hypophyseal portal blood.

beta-Endorphin was measured by RIA in the hypophyseal portal blood of six pig tailed monkeys after pituitary stalk section. The mean beta-endorphin concentration was 4,770 pg/ml (range, 2,900-10,500 pg/ml). This was more than 100 times greater than the mean simultaneous peripheral venous concentration, which was less than or equal to 45 pg/ml. After gel filtration of the portal plasma extracts, the majority of beta-endorphin immunoactivity eluted as a single peak coincident with synthetic beta-endorphin standard. The demonstration of high levels of beta-endorphin in the hypophyseal portal blood suggests that endogenous opioids of hypothalamic origin are secreted into the portal blood and may directly affect the pituitary.

Dopaminergic regulation of alpha-melanocyte-stimulating hormone and N-acetyl-beta-endorphin secretion in the fetal lamb.

alpha MSH is present in high concentrations in the intermediate lobe of the fetal pituitary and has been implicated as a regulator of fetal adrenal steroidogenesis and fetal growth. However, there are few data regarding alpha MSH levels in fetal plasma or the control of fetal alpha MSH secretion. We measured alpha MSH immunoactivity in the plasma of chronically catheterized fetal lambs (gestational age, 116-138 days), newborn lambs, and adult sheep both in the baseline state and after dopamine receptor blockade with metoclopramide. The effect of metoclopramide on the release of another proopiomelanocortin-derived peptide, N-acetyl-beta-endorphin (N-acetyl-beta EP), which is synthesized together with alpha MSH in the intermediate lobe, was also studied. Baseline fetal plasma alpha MSH was significantly greater than maternal alpha MSH [35.6 +/- 2.2 (+/- SEM) vs. 10.0 +/- 1.0 pg/ml]. In eight studies in five fetal lambs, alpha MSH rose to a peak level of 121 +/- 23 pg/ml 15 min after metoclopramide administration to the fetus. Simultaneous maternal alpha MSH levels did not change, suggesting that the alpha MSH in fetal plasma was of fetal pituitary origin. Gel filtration of pooled fetal plasma extracts revealed that the alpha MSH immunoactivity eluted in the same position as the alpha MSH standard. Metoclopramide caused the secretion of nearly equimolar amounts of alpha MSH and N-acetyl-beta EP into fetal plasma. In four fetal lambs, basal N-acetyl-beta EP levels of 156 +/- 34 pg/ml rose to 305 +/- 65 pg/ml 15 min after metoclopramide treatment. Metoclopramide also stimulated plasma alpha MSH in newborn and adult sheep. In six newborn lambs, alpha MSH rose from 45.2 +/- 13 to 211 +/- 38 pg/ml 15 min after metoclopramide treatment, whereas in four adult sheep, a basal alpha MSH level of 11.1 +/- 2.2 pg/ml rose to 20.1 +/- 2.7 pg/ml 15 min after metoclopramide. In addition, metoclopramide stimulated fetal and neonatal PRL secretion, but had no effect on plasma vasopressin concentrations or acid-base and blood gas values. These studies indicate that immunoreactive alpha MSH and N-acetyl-beta EP are secreted into ovine fetal plasma and that the secretion of these peptides in the fetus appears to be under tonic dopamine inhibition, as is the case in the adult sheep and newborn lamb.

Plasma corticotropin-releasing factor concentrations in the baboon during pregnancy.

We have studied the secretion of placental CRF during pregnancy in the baboon, an animal model with many similarities to human pregnancy. Plasma CRF was measured in two groups of animals. In group 1, studies were performed in six anesthetized animals beginning 8 days postconception. In group 2, studies were performed in five unanesthetized chronically catheterized maternal and five fetal animals in the latter third of pregnancy. In the first study beginning early in pregnancy, CRF was undetectable in all animals on days 8 and 15 postconception. Plasma CRF became detectable in two animals on day 24 and in the remaining four on day 30. Plasma CRF rose significantly to a mean of 810 +/- 160 pg/ml at 37 days gestation (F = 4.20; P < 0.001). Mean maternal plasma CRF was 2452 +/- 1120 pg/ml on day 44 and remained elevated, with a great deal of variability between subjects, until the end of the study period (128 days of gestation). Samples in this group were obtained after ketamine sedation. The effect of ketamine on CRF was studied in three chronically catheterized animals. Samples were obtained before and 2, 4, 6, and 24 h after ketamine administration (40 mg, iv). The baseline CRF concentration was 1168 +/- 131 pg/ml and did not change significantly over the time period studied. In the second study in the chronically catheterized animals, maternal plasma CRF was 1990 +/- 680 pg/ml at 131-140 days gestation and remained elevated until near term at 170 days (term = 175-180 days). Within 24 h after birth, plasma CRF became undetectable (< 60 pg/ml). CRF was also measured in chronically catheterized fetal baboons. The mean CRF concentration was 614 +/- 224 pg/ml at 131-140 days and remained in this range until the end of the period studied (151-160 days gestation). To characterize the CRF immunoactivity in maternal baboon plasma, Sephadex chromatography was performed on an 8.4-ml plasma sample obtained at 160 days gestation. The majority of the CRF immunoactivity eluted in the same position as synthetic human CRF. We conclude that high levels of placental CRF are present in the systemic circulation of the maternal and fetal baboon during pregnancy. In contrast to human pregnancy, which is characterized by an exponential rise in maternal CRF concentrations in the final weeks before delivery, an exponential rise in maternal baboon CRF concentrations occurs early in pregnancy.

Dopaminergic and serotonergic involvement in opiate-induced prolactin release in monkeys.

The present experiments were performed to determine the site of action (hypothalamic or hypophyseal) and the mechanism (dopaminergic or serotonergic) by which morphine increases PRL in monkeys (Macaca mulatta and Macaca nemestrina). To determine the site of action, 9 mg morphine were injected iv to four intact and four pituitary stalk-sectioned monkeys. PRL concentrations rose significantly (P less than 0.01) from less than 5 ng/ml to an average maximum value of 208 +/- 20 ng/ml at 15 min in intact animals, but remained unchanged in pituitary stalk-sectioned animals. There was a significant reduction (P less than 0.01) of this response in intact monkeys that received 5 mg L-dopa, iv, 5 min before the morphine stimulus. In these animals, PRL only rose to 100 +/- 46 ng/ml. In contrast, the PRL response in four monkeys pretreated with 5 or 20 mg methysergide, iv (a serotonin receptor blocker), 5 min before the opiate stimulus was not different from in controls. Likewise, the daily administration of 100 mg p-chlorophenylalanine, sc (a serotonin synthesis blocker), for 6 days failed to alter the PRL response to morphine. These data suggest that opiates increase PRL via a neural site of action and that the mechanism may involve dopaminergic but not serotonergic pathways.

Effects of leptin receptor mutation on Agrp gene expression in fed and fasted lean and obese (LA/N-faf) rats.

Agouti-related protein provides an orexigenic signal, probably through interaction with central melanocortin receptors. Expression of Agrp is markedly increased in the hypothalamus of mice deficient in leptin (Lep(ob)/Lep(ob)) or its receptor (Lepr(db)/Lepr(db)), suggesting that leptin mediates signals suppressing Agouti-related protein production. The regulation of Agrp expression in the rat hypothalamus has not been reported. We, therefore, analyzed the expression of Agrp in the medial basal hypothalamus of lean (+/+, +/fa(f)) and obese leptin receptor-deficient (fa(f)/fa(f)) LA/N rats. Using a sensitive solution hybridization/S1 nuclease protection assay, we found no significant difference in Agrp messenger RNA (mRNA) levels (pg/microg total RNA +/- SEM) in obese rats (n = 5), compared with lean controls (n = 5): 0.46 +/- 0.06 vs. 0.47 +/- 0.06 (P = 0.9). Similarly, no difference in Agrp expression was found using in situ hybridization or semiquantitative RT-PCR. In contrast to Agrp, Pomc mRNA levels were significantly suppressed in the obese, compared with the lean, rats (P = 0.001). Thus, the ratio of Pomc to Agrp mRNA is decreased in the obese rats and may be an important modulator of food intake. To assess the physiological regulation of Agrp in rats, we examined the effect of food deprivation in lean Sprague Dawley (SD) rats. There was a 273% increase in medial basal hypothalamus Agrp mRNA in SD rats fasted for 48 h (n = 8), compared with rats fed ad libitum (n = 8): 0.82 +/- 0.23 vs. 0.30 +/- 0.08 (P = 0.0001). Lean LA/N rats (n = 7) fasted for 48 h also showed a 231% increase in Agrp expression, compared with fed lean controls (n = 8): 0.74 +/- 0.11 vs. 0.32 +/- 0.03 (P = 0.002), whereas Pomc expression was decreased by 32% in fasted animals from the same experiment (0.34 +/- 0.05 vs. 0.50 +/- 0.07; P = 0.03). There were no significant differences in Agrp or Pomc mRNA levels between fasted and fed obese LA/N-fa(f) rats. These results suggest that, in the rat, the Agrp response to fasting may involve leptin-mediated phenomena, but factors in addition to leptin must also be involved in the regulation of Agrp gene expression.

Measurement of beta-endorphin in human plasma.

beta-endorphin has been identified in human plasma by means of gel filtration and a sensitive radioimmunoassay for human beta-endorphin (beta h-endorphin). Mean baseline plasma beta h-endorphin concentration in 5 individuals was 21 +/- 7.3 (SD) pg/ml (6.2 +/- 2.2 (SD) fmole/ml). Following metyrapone stimulation mean plasma concentration increased to 55.4 +/- 10.1 (SD) pg/ml (16.3 +/- 3.1 (SD) fmole/ml). The molar ratio of human beta-lipotropin (beta h-LPH) to beta h-endorphin was 2.2 in baseline plasma and 2.4 after metyrapone stimulation.

Clinical review 110: Diagnosis and treatment of pituitary tumors.

We are fortunate to have multiple safe and effective therapeutic options available for the treatment of pituitary tumors. These options include medical therapy, transsphenoidal surgery and radiotherapy. The treatment of choice depends on the type of pituitary tumor. The majority, of PRL-secreting tumors can be effectively treated with dopamine agonists. Transsphenoidal surgery is also an effective option for patients who are resistant to or intolerant of these drugs. Transsphenoidal surgery remains the treatment of choice for the majority of patients with GH, ACTH, and TSH-secreting tumors and for large nonsecreting tumors. Medical therapy with somatostatin analogs and/or dopamine agonists should be undertaken in patients with persistent elevations of GH and IGF-I levels; radiotherapy should be considered for patients with significant residual tumor in whom medical therapy is unsuccessful. Radiotherapy is also indicated for ACTH-secreting tumors not cured by surgery; medical therapy with ketoconazole and other adrenal enzyme inhibitors can be used as adjunctive therapy to lower cortisol levels. Postoperative radiotherapy for nonsecreting tumors is also an option if there is considerable residual tumor or evidence of tumor growth on follow-up MRI. Evaluation and treatment of hypopituitarism is an important part of the management of all patients with pituitary tumors. Patients also should be monitored for the development of new deficits, particularly after radiotherapy. The development of new medical therapies, such as GH antagonists, as well as refinements of surgical, radiotherapy, and imaging techniques should continue to improve our management of pituitary tumors.