Diurnal pattern of stress-evoked neurohypophyseal hormone secretion: sexual dimorphism in rats.
Levels of oxytocin (OT) and arginine-vasopressin (AVP) in plasma of control or immobilized male and female rats were determined at various times of the day. Control levels of the neurohypophyseal peptides did not exhibit diurnal variation. Raised plasma levels of OT were found following immobilization at all times in both males and females, and a significant diurnal variation in stressed levels of OT was also observed, but in male rats only. Thus the morning stress responses (07.00 and 09.00 h) of males were markedly greater than the midday and evening responses, whereas the responses of females were similar throughout the day. A similar pattern was evident for AVP although plasma levels of AVP were not consistently elevated by stress. These findings provide further evidence of sexual dimorphism in both the regulation of neurohypophyseal stress responses and the periodicity of diurnal rhythms.
D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism*; D002940:Circadian Rhythm; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism; D005260:Female; D007031:Hypothalamus / Q000378:metabolism; D008297:Male; D010121:Oxytocin / Q000378:metabolism*; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D051381:Rats; D012149:Restraint, Physical; D012727:Sex Characteristics; D013312:Stress, Physiological / Q000378:metabolism*
D001127:Arginine Vasopressin; D010121:Oxytocin; D003346:Corticotropin-Releasing Hormone