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S. N. Thornton, G. Leng, R. J. Bicknell, C. Chapman and T. Purdew

ABSTRACT

Plasma samples obtained at 4-h intervals from goats for at least 24 h before and then during 24 h of deprivation of water were analysed by radioimmunoassay for vasopressin and oxytocin concentrations. The samples were also analysed for osmolality and sodium concentration. The differential effect of night/day versus day/night deprivation was also studied. During the two periods before the two deprivations osmolality varied in a regular manner, with low values occurring at 08.00 h. Sodium concentration followed osmolality, whereas vasopressin did not vary during the period before deprivation. During deprivation vasopressin increased along with osmolality and sodium concentration, with the beginning of the increase occurring after the morning feed. Oxytocin levels did not increase during the period of deprivation.

These results do not support the hypothesis of general release of neurohypophysial hormones in response to osmotic stimuli but instead indicate there are species variations with respect to hormonal response to water deprivation.

J. Endocr. (1986) 110, 335–340

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R. F. Parrott, S. N. Thornton, M. L. Forsling and C. E. Delaney

ABSTRACT

The effect of stress on drinking, water balance and endocrine profile was studied using ten castrated rams. Individual sheep were exposed to 30-h periods of total isolation (psychological stress) or physical separation from their social group (control). Plasma was analysed for haematocrit, osmolality, electrolyte levels and concentrations of cortisol and arginine vasopressin. Isolation stress significantly reduced water intake, increased haematocrit and plasma concentration of cortisol, but did not alter osmolality or vasopressin concentration. The physiological effects of this self-imposed water restriction contrast with those obtained by depriving the sheep of water for 24 h under conditions that were not stressful, i.e. by keeping them grouped together. These results suggest that cortisol may act to defend plasma volume in sheep exposed to acute stress. The results also indicate that vasopressin probably should not be considered to be a 'stress hormone' in the sheep.

J. Endocr. (1987) 112, 305–310