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 preparatThe somatomedin-like peptide multiplicationstimulating activity (MSA) binds specifically to rat serum. The pattern of MSA binding is GH dependent. Specific binding of [l25I]iodo-MSA in normal rat serum is primarily in the y-globulin region (peak II) on Sephadex G-200, while MSA binding in hypophysectomized (hypox) rat serum is near the albumin region (peak III). This study further characterizes the peak II and peak III somatomedin-binding proteins in rat serum and compares them with somatomedin-binding proteins produced by rat liver cells in culture. [l25I]Iodo-MSA binding to normal rat serum is abolished by trypsin pretreatment of rat serum, suggesting that MSA binds to protein components of serum. The only detectable somatomedin activity (measured by [3H]thymidine incorporation into chick embryo fibroblast DNA) in fractions of normal rat serum chromatographed on Sephadex G-200 coincides with peak II binding of [125I]iodo-MSA. In hypox rat serum, the majority of detectable somatomedin activity is in the peak III region. There is complete displacement of the human somatomedins [l25I]iodoinsulin-like growth factor I and II and [l2r>I]iodosomatomedin A from the rat serum-binding sites by unlabeled MSA, suggesting that the human somatomedins bind to the same sites as MSA. Treatment of normal rat serum with 1 M acetic acid dissociates somatomedin activity from its binding proteins and converts somatomedin-binding proteins from peak II to peak III. Scatchard analysis of competitive binding data using [125I]iodo- MSA yields a binding affinity that is not appreciably different for either normal or hypox rat sera. The binding capacity of normal or acid-treated normal rat serum for MSA is significantly greater than that for comparabVitamin D3 in rachitic chicks stimulates calcium absorption and induces the synthesis of two pools of intestinal calcium-binding protein (CaBP), one soluble and the other membrane bound. Cortisol acetate caused a decrease in calcium absorption which was accompanied by a decrease in soluble CaBP. Cortisol was similarly effective in 1, 25-dihydroxyvitamin D3-dosed chicks, suggesting that the glucocorticoid effect was not entirely due to the defective synthesis of this metabolite. Ca absorption was directly correlated with soluble CaBP and alkaline phosphatase and inversely related to the ratio of bound to soluble CaBP. It was further observed that the slope of the Ca absorption vs. soluble CaBP regression line was greater in chicks given 1, 25-dihydroxyvitamin D3 compared to those given vitamin D3, and this is interpreted to mean that another factor or condition, in addition to assayed concentrations of soluble CaBP, determines the degree of calcium absorption. © 1979 by The Endocrine Society.
