The hypothesis that 17β-estradiol suppresses dopamine secretion into hypophysial portal blood was tested. Portal plasma concentrations of dopamine were significantly lower in proestrous rats (1.0 ± 0.1 ng/ml; mean ± SE) than in estrous rats (1.9 ± 0.38 ng/ml). To deplete the animal of endogenous steroid hormones, proestrous rats were adrenalectomized (Adx) and ovariectomized (Ovx). Twenty-four hours later, hypophysial portal blood was collected for 60 min, and the plasma from this blood was analyzed for dopamine. Arterial plasma from these rats was assayed for 17β-estradiol and progesterone. The concentrations of dopamine in the portal plasma of sham-operated rats and bilaterally Adx-Ovx rats were similar to those in estrous animals. The concentration of dopamine in portal plasma of Adx-Ovx rats injected 24 h earlier with 50 μg 17β-estradiol was 1.0 ± 0.31 ng/ml, which was comparabExposure of adipocytes from young rats (2–3 months old) to dexamethasone in vitro results in 40–50% inhibition of glucose transport and metabolism. ComparabDose-response curves were obtained for the production of androgen-binding protein (ABP) by Sertoli cells prepared from testes of 20-day-old rats and treated in culture with either FSH or testosterone (T). FSH stimulated ABP production by up to 3.5 times control levels. For NIH-FSH-Sll, the ED50 was 3 ng/ml, and for highly purified ovine FSH, the ED50 was 0.066 ng/ml. Addition of T produced a stimulation of up to 3 times control levels; half-maximal response was obtained at a dose of 4 nM. The presence of small numbers of contaminating Leydig cells in some preparations resulted in production of endogenous T, especially when high doses of NIH-FSH, which contains some LH, were employed. A modified preparatDissociation of [125I]iodoinsulin from adipocyte insulin receptors was studied in the presence or absence of the insulin derivatives, desoctapeptide insulin and desalanine desasparagine insulin. When cells were allowed to associate with a tracer concentration (10-10 M) of [125I]iodoinsulin and dissociation was studied in either insulin-free buffer or buffer containing 100 ng/ml unlabeled insulin, dissociation was accelerated in the presence of unlabeled insulin. This is consistent with negatively cooperative site-site interactions. On the other hand, when dissociation studies were performed in the presence of high concentrations of desoctapeptide insulin or desalanine desasparagine insulin, dissociation rates were slower than those observed in insulin-free buffer. In marked contrast, when cells were allowed to achieve a high fractional receptor occupancy by associating with high concentrations of either desoctapeptide insulin or desalanine desasparagTo study the relationship between formation and release of Golgi-derived secretory granules and progesterone secretion, slices of ovine luteal tissue were incubated in the presence of LH and/or calcium ionophore A23187. Increases in progesterone secretion in response to LH and/or ionophore were accompanied by a concomitant release of secretory granules. In contrast, in the presence of colchicine, LH-stimulated progesterone secretion was significantly reduced (P < 0.01), granule formation appeared to be blocked, and there was little evidence of exocytosis. In addition, unusual pleomorphic membranebounded saccules containing an electron-dense material were abundant throughout the centrospheric region of cells treated with colchicine. Because of the close paralEffects of ionophore A23187 on skeletal collagen formation were investigated in vitro. Collagen synthesis was quantitated in fetal rat calvaria by measuring [3H]proline incorporation into collagenase-digestible (CDP) and noncollagen protein (NCP) using purified bacterial collagenase; [3H]proline was added for the last 2 h of culture. Results are as follows. 1) A23187 (0.03–1.0 jug:/ml) inhibited incorporation of label into CDP and NCP after 24 h of culture, with a greater effect on CDP. The response was not associated with altered amino acid uptake, precursor pool size, or degradation of newly labeled protein. 2) Submaximal concentrations of A23187 and parathyroid hormone or dibutyryl cAMP decreased CDP formation to a greater extent than treatment with the agents alone. 3) Imidazole, while ineffective by itself, enhanced the effect of A23187. 4) Alteration of medium calcium did not affect the response to ionophore. 5) The inhibitory effect of A23187 was partially reversed by 24 h and completely reversed by 48 h of control treatment subsequent to an initial 24-h incubation with ionophore. 6) Indomethacin had no effect on CDP or NCP formation, either in the presence or absence of A23187. 7) A23187 did not alter the uptake of [3H]thymidine or [3H]uridine into acid-extractable pools but decreased incorporation of label into DNA and RNA, respectively. 8) Histological examination showed no difference between control and A23187 treatment after 24 h. We conclude that A23187 decreases bone collagen and noncollagen protein synthesis, possibly through a calcium-mediated effect. The mechanism of the inhibitory effect on DNA and RNA labeling is unknown, although it may be related to calcium. Our results further suggest that calcium may be involved in the actions of paratThese studies examine the metabolism of highly purified bovine parathyroid hormone [bPTH-(l–84)] by fetal rat calvaria. Enzymatically dispersed bone cells and intact (minced) calvaria were incubated with bPTH-(l–84) and the incubation medium was analyzed for degradation of PTH by polyacrylamide gel electrophoresis. Eluates of gel slices were assayed for immunoreactive PTH (iPTH) in carboxy- and amino-terminal RIAs. Both bone preparations metabolized bPTH-(l–84). The intact hormone progressively decreased with time and carboxyterminal iPTH fragments were evident by 5 min of incubation. In the isolated cell preparations, intact hormone was completely degraded at submaximal doses of PTH (5 × 10-9 M), as assessed by cAMP production. Degradation was incomplete in intact calvarial preparations at all doses studied. Intact calvaria were less sensitive to PTH with regard to cAMP production. No amino-terminal fragments were detected in the medium with either cell preparation. Oxidized (biologically inactive) bPTH- (1-84) was not metabolized in these systems. These findings contrast with studies in liver and kidney preparatA single injection of 10-4 pg synthetic arginine vasotocin (AVT) into the third ventricle of urethane anesthetized male rats, significantly decreased plasma LH levels between 15–60 min after the injection, while plasma FSH levels remain unchanged. At 120 min, plasma LH levels returned to their preinjection levels. In the range tested, the effects of AVT seem to be dose dependent, because 10-5 pg induce a less pronounced decrease of plasma LH levels than 10-4 pg, and 10 pg did not decrease plasma LH levels. No effects on plasma LH levels could be detected when amounts of AVT between 10-1–10-4 pg were injected into the pituitary. Neither synthetic arginine vasopressin nor oxytocin, injected into the third ventricle in amounts between 10-3–10-4 pg, was able to affect plasma LH levels. The increase of plasma LH levels induced by exogenous LHRH was not significantly affected by the previous intraventricular injection of AVT. When 10-4 pg AVT were injected into the third ventricle of rats treated 48 h earlier with p-chlorophenylalanine (p-CPA), no effects on plasma LH levels could be detected. Administration of 5-hydroxytryptophan to p-CPA-treated rats, 1 h before the injection of AVT partially restored the ability of AVT to decrease plasma LH levels. The hypothalamic 5-hydroxytryptamine (5-HT) content of normal rats as well as that of rats treated with p-CPA and 5-hydroxytryptophan significantly increased at 30 min after the intraventricular injection of 10-4 pg AVT. No effects on hypothalamic 5-HT content could be detected after the intraventricular injection of 10-4 pg AVT in rats treated with p-CPA alone. The results of the present work suggest that AVT injected into the third ventricle of male rats at the lowest effective concentrations so far reported for an active biological substance decreases plasma LH levels by inhibiting the release of LHRH in the brain and not by interfering directly with the release of LH at the pituitary level. Evidence is provided that AVT induces these effects by interfering with 5- HT neurotransmission in the brain. © 1979 by The Endocrine Society.
