Water and Electrolyte Excretion During the Oestrous Cycle in Sheep

Abstract

Electrolyte excretion was observed during 24 oestrous cycles in housed sheep, together with mixed salivary Na/K ratio during 10 additional cycles. 1. The sharp fall in food and fluid intake at oestrus accompanied a peak of sodium excretion which changed to peak retention 3 days later, both in faeces and urine. 2. Potassium excretion declined with food intake at oestrus but subsequently failed to recover to pre-oestrous levels dispite full recovery of dietary intake. 3. Curiously, water intake also recovered completely whereas urinary and faecal water retention continued; faecal loss actually exceeded renal excretion on these liberal water intakes. 4. Changes in salivary, urinary and faecal Na/K indicated an aldosterone peak neither during the luteal phase nor at oestrus but three days later. The data rarse questions concerning the regulation of water and electrolyte balance within the normal cycle. They also provide a baseline for the investigation of renal effects of gonadal steroids. Possible roles for aldosterone, ADH and progesterone in maintaining fluid and electrolyte balance are discussed, emphasising problems confronting species which have evolved with heavy obligatory potassium excretion but undependable supplies of sodium and water.Sheep vary their sodium intake during the oestrous cycle, taking least at oestrus and most at the climax of the luteal phase [Michell, 1975]. This seemed consistent with the idea that oestrogens stimulate salt retention whereas progesterone promotes natriuresis [Landau, 1973], but specific data in sheep were lacking.Salt retaining effects of oestrogens were suspected almost as soon as those of adrenal steroids [Thorn, Nelson and Thorn, 1938] but considerable conflict emerges from the literature on gonadal steroids and electrolyte excretion [Christy and Shaver, 1974;Lindheimer and Katz, 1977]. The factors influencing aldosterone levels during the human cycle remain uncertain [Schwartz, 1975]. The luteal rise can be attributed to sodium loss induced by progesterone but the rise near ovulation is less easily explained [Sundsfjord and Askvaag, 1973]. Such questions have practical significance since the aetiology of both premenstrual tension and contraceptive hypertension remain uncertain

Acclimation to a High‐Salt Diet Is Sex Dependent

“…Earlier studies have reported changes in urinary excretion of aldosterone and norepinephrine during the estrus cycle in sheep and rats, respectively. 43 , 44 , 45 In addition, ET A and ET B mRNA expression and nitric oxide synthase activity in female rat kidneys are regulated by estradiol. 46 , 47 Accordingly, we anticipate that the increased variability in the urinary excretion levels of Na + ‐regulatory factors in female rats would be related to different phases of the estrus cycle.…”

No Time To Eat: An Adaptationist Account Of Periovulatory Behavioral Changes

“…The by-product explanation is weakened, however, by the observation that ovulation is accompanied by parallel declines in other ingestive behaviors. In rats (Tarttelin and Gorski 1971;Eckel et al 2000), pigs (Friend 1973;Rollin et al 1989), sheep (Tarttelin 1968;Michell 1979), cows (Macfarlane 1967), and, apparently, humans (Fong and Kretsch 1993), water intake exhibits the same cyclic changes as food intake. Although food intake and water intake are generally behaviorally linked (Engell 1988;Mathis et al 1996), the periovulatory reduction in water intake is not a secondary consequence of the reduction in food intake, but rather reflects changes independent of those responsible for the decrease in feeding.…”

“…Because these societies are all related, however, available results do not allow us to rule out such a possibility. More persuasive, therefore, is the observation that the same pattern occurs in a wide variety of other mammals: a peri-estrus nadir in food intake occurs in chacma baboons (Bielert and Busse 1983), rhesus macaques (Czaja 1975;Rosenblatt et al 1980;Mello et al 1986;Kemnitz et al 1989), owl monkeys (Rauth-Widmann et al 1996), dogs (Houpt et al 1979), pigs (Friend 1973;Rollin et al 1989), goats (Forbes 1971), sheep (Tarttelin 1968;Michell 1979), deer (Wong and Parker 1988), cows (Raun et al 1967), guinea pigs (Czaja and Goy 1975), and rats (Tarttelin and Gorski 1971;Drewett 1974;Blaustein and Wade 1976;Eckel et al 2000).…”

Cerebral Regulation of Thirst

“…Daily fluid intake changes over the course of the estrus cycle in animals, and this is abolished by oophorectomy [104,105]. Water and food intake fall at estrus, and this effect is preceded by a high level of circulating estrogen.…”