摘要:

The activities of NAT and HIOMT and the melatonin concentration in the Harderian glands of intact, gonadectomized, and gonadally-regressed male Syrian hamsters were studied. To produce gonadal regression, hamsters were exposed to either artificial or naturally short photoperiods. NAT activity of castrated and gonadally-regressed hamsters was always less in comparison to that of animals with intact gonads. Castrated hamsters exposed to long days showed higher NAT activity than that of castrated animals exposed to short photoperiods indicating that light may have some influence on Harderian NAT independent of the gonadal status. Also, gonadally-regressed hamsters exposed to long photoperiods exhibited higher NAT activity in comparison to gonadally-regressed animals exposed to short days. The HIOMT activity and melatonin content of Harderian glands in all these groups of male Syrian hamster were very low.

ISSN:0743-5800    

DOI:10.3109/07435808809032981

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

We have developed a redox-chemical delivery system for brain-enhanced drug delivery of estradiol based on an interconvertible dihydropyridine⇌pyridinium salt carrier. Estradiol, when combined with the carrier, readily crosses the blood-brain barrier and upon oxidation of the carrier is“locked”in the brain. The aim of this study was to evaluate the effects of the estradiol-chemical delivery system (E2–CDS) on body weight change and associated alterations in the secretion of anterior pituitary hormones in middle-aged, male rats. The data revealed that rats receiving E2–CDS exhibited a significant weight loss by 2 days which continued to day 14, the last observation day. A significant weight difference was observed between E2–CDS and DMSO-treated animals. Serum estradiol levels of rats treated with E2–CDS were elevated 100–fold by day 1 and decreased thereafter and serum prolactin concentrations were doubled by 24 hours and continued to increase to the completion of the experiment. Testosterone levels were markedly suppressed by 24 hours while serum levels of LH, TSH, T3, T4 and GH were not significantly altered. These data indicate that the E2–CDS causes a long-term reduction in body weight and testosterone secretion and that these changes are not mediated by alterations in the secretion of anterior pituitary hormones.

ISSN:0743-5800    

DOI:10.3109/07435808809032982

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

Activation of calcium-activated, phospholipid-dependent protein kinase C by phorbol esters such as 12–0–tetradecanoyl-phorbol-13–acetate (TPA) has been shown to mediate release of hormones in many systems. To investigate the role of protein kinase C in the mechanism of pituitarv ACTH release, we studied the effect of the following conditions on TPA mediated ACTH release in primary rat pituitary cultures; corticotropin releasing hormone (CRH), different concentrations of extracellular calcium (Ca+2), nifedipine (a calcium channel blocker), PGE2and cortisol (regulators of ACTH secretions). TPA induced ACTH release in a dose dependent fashion with an ED50of 4.2×10–10M. The maximal amount of ACTH release individually induced by TPA (10–8M) and CRH (10–8) were identical. TPA (10–8) potentiated the amount of ACTH release from cells already maximally stimulated with CRH (4×10–8M). TPA mediated ACTH release was dependent on extracellular calcium and inhibited by nifedipine, to a maximum of 35%. Cortisol decreased the amount of ACTH individually released by TPA and CRH in a similar and dose dependent fashion with maximal inhibition of 47% occurring at 10–7M. PGE2caused a dose dependent reduction of TPA mediated ACTH release. In conclusion, the pathways of ACTH release induced by CRH and TPA are not entirely the same but may share a common regulatory pathway. Extracellular calcium and calcium cell influx may be important for maximal ACTH release induced by TPA. Protein kinase C activation may play an important role in CRH stimulated ACTH release.

ISSN:0743-5800    

DOI:10.3109/07435808809032983

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

The crystal and molecular structures of 3,5,3′–triiodothyropropionic acid (T3P), determined as an N-diethanolamine salt, were carried out and the results are compared with those of other thyroid hormone structures. These data show that T3P has an unusual conformation with the diphenyl ether bridge outside the range normally observed for other thyroactive acid structures and has the largest deviations from the ideal skewed conformation predicted for 3,5–diiodothyroactive compounds. These conformational properties are not observed in the structures of thyroformic or acetic acid analogues. Biochemical data indicate that thyropropionic acid analogue activity differs from that of other acid analogues which could imply that their metabolism and activity can be controlled differently from that of other hormone metabolites.

ISSN:0743-5800    

DOI:10.3109/07435808809032984

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

The present communication documents LH- and forskolin–-induced activation of adenylate cyclase (AC) system and progesterone synthesis in corpora lutea from pregnant ewes. The activation of AC in plasma membranes by LH or forskolin was amplified by Gpp(NH)p. These results suggest that regulatory nucleotide component (Ns) of the AC complex is required for full expression of the maximal response of ovine luteal AC to forskolin. Simultaneous addition of maximal concentrations of forskolin (10–4M), Gpp(NH)p (10–4M) and LH (10–7M) led to greater than additive (i.e. synergistic) responses: the experimental value was 4.71±0.19 nmoles cAMP/mg of membrane protein, whereas the theoretical additive effect was 3.17±0.10 nmoles/mg of membrane protein (p<0.001). These data reveal that more Nsor C component is being activated in these cells when combined treatments with these agents are applied.In intact cells maximum stimulatory concentrations of forskolin or LH caused similar increase in progesterone production with similar time courses. In striking contrast, the exposure of the luteal cells to LH and forskolin simultaneously led to a decrease in progesterone synthesis as early as 1h30 (40 %, p<0.001). Thus, the synergism observed between LH and forskolin on the stimulation of plasma membranes AC activity did not occur in steroidogenesis. The AC responses in crude plasma membranes form these cells to different stimulants were enhanced (i.e. 15%, p<0.2 for Gpp(NH)p, 33%, p<0.01 for LH plus Gpp(NH)p and 52%, p<0.01 for forskolin). These findings suggest that an early desensitization of the AC system cannot explain the impaired steroidogenic response observed.

ISSN:0743-5800    

DOI:10.3109/07435808809032985

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

The gastrointestinal tract interacts actively with the thyroid hormones, T4 and T3. Both T4 and T3 are absorbed well but incompletely from the gut, and many factors affect this absorption. The mechanism of absorption is unknown. It is decreased in most malabsorption conditions, but is increased in the postgastrojejunotomy syndrome. It may involve conjugation to the glucuronide forms (T4G and T3G) in the mucosal cell with subsequent deconjugation prior to appearance in the portal vein blood. Absorption appears to be reduced in the presence of excess T4, and increased in hypothyroidism. The liver takes up a large fraction of the T4 and T3 from its circulation and returns a portion of the portal hormone back to the gut via the bile. There is also direct T4 and T3 secretion into the gut from the mesenteric circulation. Recent studies suggest that the gut plays a major role as a reservoir for the thyroid hormones, especially for T3, and that it may also play a role in the regulation of hormone activity.

ISSN:0743-5800    

DOI:10.3109/07435808809032986

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor