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The neural lobe of the golden hamster contains one major and two minor proteins. The major protein was identified as a neurophysin in view of its electrophoretic properties, its high cysteine content and its depletion from the neural lobe upon saline imbibition.
The depletion of neurophysin and vasopressin from the neural lobe and the alterations of several indices of dehydration in the blood of the hamster were less than those found in the rat upon saline imbibition, suggesting that the hamster has a greater ability to adapt to conditions in which water is scarce.
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SUMMARY
Uptake of tritiated lysine vasopressin ([3H]LVP) was studied in halved neural lobes of rats (which had been given either tap water (control group) or 2% (w/v) NaCl solution as drinking water for 4 days) as well as in slices of pig neural lobe. Uptake of radioactivity into the neural lobes was shown but analysis of the extracts of incubated lobes of both species by ion exchange chromatography showed that very little of it remained in the tissue as hormone. In addition, some radioactivity was associated with trichloroacetic acid-insoluble proteins.
After 90 min of incubation, and after correction for the breakdown, the uptake of unchanged [3H]LVP, expressed as a tissue: medium ratio, was 0·14 ± 0·04 and 0·09 ± 0·03 (mean ± s.e.m.) for the saline-treated and control rats respectively, while the tissue: medium ratios for the breakdown product(s) were 6·47 ± 0·45 and 5·50 ± 0·36. The results suggest uptake of [3H]LVP into the cell with almost complete intracellular breakdown of the hormone.
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Radioactivity accumulates in the posterior pituitary after intravenous injections of [3H]oxytocin (Aroskar, Chan, Stouffer, Schneider, Murti & du Vigneaud, 1964) or tritiated lysine vasopressin ([3H]LVP) (Willumsen & Bie, 1969). These results allow for the possibility that the neurohypophysial hormones may be taken up by the pituitary after the release of endogenous, or the administration of exogenous, oxytocin and vasopressin. The experiments in vitro of Pliška, Thorn & Vilhardt (1971) and Edwards (1971) showed that uptake of radioactivity occurred after incubation of neural lobes with labelled vasopressin but that much of the activity was not associated with hormone. The present communication describes a study on the uptake of [3H]oxytocin by neural lobes of rats incubated in vitro.
Halved neural lobes were incubated in a bicarbonate buffer (McIlwain & Rodnight, 1962) containing [3H]oxytocin (prepared in the Departement de Biologie, Commissariat à l'Energie Atomique, France) and non-radioactive purified oxytocin
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In earlier studies it was shown that oxytocin and vasopressin were broken down by peptidases present in the neurohypophyses of the rat, pig and ox (Edwards, 1971a, b; Pliška, Thorn & Vilhardt, 1971). The present work was carried out to determine the subcellular localization of this enzymic activity with special interest in the lysosomes whose function as a mechanism of controlling excess hormone in the anterior pituitary has been suggested by Smith & Farquhar (1966).
Separation of the various subcellular fractions was carried out using a differential centrifugation procedure suggested by A. Livingston (personal communication). Four fractions were prepared: A (1000 g for 10 min), B (5000 g for 10 min), C (25 000 g for 20 min) and D (the final supernatant). Each fraction was analysed for vasopressin (hormonal marker), cathepsin (lysosomal marker), fumarase (mitochondrial marker) and lactate dehydrogenase (cytoplasmic marker). Complete separation into discrete fractions was not
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Andrology Laboratory, ANZAC Research Institute, University of Sydney, Concord Hospital, Sydney, New South Wales, Australia
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Laboratory for Ageing Research, School of Medical Sciences, University of New South Wales Sydney, New South Wales, Australia
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Andrology Laboratory, ANZAC Research Institute, University of Sydney, Concord Hospital, Sydney, New South Wales, Australia
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As the mechanistic basis of polycystic ovary syndrome (PCOS) remains unknown, current management relies on symptomatic treatment. Hyperandrogenism is a major PCOS characteristic and evidence supports it playing a key role in PCOS pathogenesis. Classically, androgens can act directly through the androgen receptor (AR) or, indirectly, following aromatization, via the estrogen receptor (ER). We investigated the mechanism of androgenic actions driving PCOS by comparing the capacity of non-aromatizable dihydrotestosterone (DHT) and aromatizable testosterone to induce PCOS traits in WT and Ar-knockout (ARKO) mice. DHT and testosterone induced the reproductive PCOS-like features of acyclicity and anovulation in WT females. In ARKO mice, DHT did not cause reproductive dysfunction; however, testosterone treatment induced irregular cycles and ovulatory disruption. These findings indicate that direct AR actions and indirect, likely ER, actions of androgens are important mediators of PCOS reproductive traits. DHT, but not testosterone, induced an increase in body weight, body fat, serum cholesterol and adipocyte hypertrophy in WT mice, but neither androgen induced these metabolic features in ARKO mice. These data infer that direct AR-driven mechanisms are key in driving the development of PCOS metabolic traits. Overall, these findings demonstrate that differing PCOS traits can be mediated via different steroid signaling pathways and indicate that a phenotype-based treatment approach would ensure effective targeting of the underlying mechanisms.
