Effect of ovariectomy and treatment with ovarian steroids on vasopressin release and fluid balance in the rat

Abstract

Plasma vasopressin concentrations have previously been shown to vary during the oestrous cycle of the rat, being highest on the morning of pro-oestrus and lowest on dioestrus day 1. To determine the effect of gonadal steroids on vasopressin secretion and fluid balance, mature rats were ovariectomized and given oestrogen, progesterone or vehicle alone s.c. for periods of up to 16 days. Plasma vasopressin concentrations fell after ovariectomy and this was reflected in an increase in 24-h urine volume. The normal increase in plasma vasopressin concentrations seen over day-light hours was also suppressed. The change in vasopressin concentrations observed on steroid treatment depended upon both the dose and the duration. High doses of oestrogen were associated with a fall in plasma vasopressin, probably as a result of fluid retention. Thus, of an initial group of rats given silicone elastomer implants containing 50, 500 or 1000 micrograms oestradiol in oil, plasma vasopressin concentrations were reduced after 7 days treatment with 1000 micrograms oestradiol implants in association with reduced plasma sodium concentrations. Daily s.c. injections of 100 micrograms oestradiol benzoate/100 g body weight produced an immediate small increase in plasma vasopressin concentrations, but by 14 days the plasma concentrations of 0.7 +/- 0.16 pmol/l (mean +/- S.E.M.) had fallen significantly and were less than those in the vehicle-treated group (1.2 +/- 0.26 pmol/l). However, after treatment for 14 days with implants containing only 50 micrograms oestradiol, plasma vasopressin concentrations were higher compared with the group receiving vehicle alone, despite the fact that the plasma osmolality was lower in the latter group, suggesting a long term resetting of the osmoreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrogen receptors: Their roles in regulation of vasopressin release for maintenance of fluid and electrolyte homeostasis

“…Estradiol replacement caused a decrease in ERβ in magnocellular neurons of ovariectomized rats [86]. Based on our evidence that ERβ expression in SON mediates inhibition of VP secretion from HNS explants, a decrease in ERβ expression induced by treating ovariectomized female rats with estradiol would be expected to cause an increase in plasma VP as reported by Skowsky et al [68] and Peysner and Forsling [51] (Table 1). The question then arises, are the dehydration-induced changes in ERβ secondary to dehydration-induced changes in circulating gonadal steroids?…”

“…For example, the E2-induced increase in pVP reported by Skowsky et al [68] in female rats could reflect predominance of ERα-mediated enhanced osmosensitivity while the lack of effect of estrogen reported by Crofton et al [7] could reflect a balance between ERα enhanced osmosensitivity and ERβ-mediated inhibition at the VP neurons. Similarly, the biphasic dose response reported by Peysner and Forsling [51] may reflect differences in the effective concentration of estrogen at ERα in SFO, OVLT, and MnPO versus ERβ in SON and PVN magnocellular VP neurons, and therefore a shift in the balance between positive and negative estrogen effects on VP secretion. However, it could also reflect differences in the effect of estrogen on target tissues and therefore, the feedback signals regulating VP secretion.…”

“…Reports on fluctuations in pVP associated with the estrus or menstrual cycle also yielded inconsistent results. Although Skowsky observed fluctuations in VP during the estrus cycle [68], others reported no effect [7] or reported that the magnitude of the diurnal fluctuation in pVP was influenced by the estrus cycle [51]. In women, an early study reported midcycle increases in pVP, but this was not confirmed in other studies [81,91,94,101].…”

“…Peysner and Forsling reported that ovariectomy caused a decrease in pVP and a suppression of the diurnal variation in pVP [51]. They observed a dose dependent effect of estrogen replacement with a high dose decreasing pVP and a low dose increasing pVP [51]. Similarly divergent results were reported in women with estrogen administration to anovulatory or postmenopausal women having no effect or causing an increase in pVP [19,101].…”

“…However, in female rats, Crofton, et al reported no change in pVP with estrogen treatment alone, but a decrease in pVP following combined administration of estrogen and progesterone [7,68]. Peysner and Forsling reported that ovariectomy caused a decrease in pVP and a suppression of the diurnal variation in pVP [51]. They observed a dose dependent effect of estrogen replacement with a high dose decreasing pVP and a low dose increasing pVP [51].…”