Effect of pinealectomy on the plasma concentrations of prolactin, cortisol and testosterone in sheep in short and skeleton long photoperiods

Abstract

Two experiments were carried out to investigate the effects of pinealectomy on the responses of prolactin, cortisol and testosterone to skeleton long photoperiods (7 h light: 10 h darkness: 1 h light: 6 h darkness; 7L: 10D: 1L: 6D) compared with short photoperiods (8L: 16D) in lambs. The first experiment included 23 female Suffolk cross sheep aged 10 months, of which six were pinealectomized. The skeleton long photoperiod significantly increased plasma levels of prolactin but this was blocked by pinealectomy; there was a peak around dusk and a trough around dawn and at the time of the 1-h period of light. There was no effect of either photoperiod or pinealectomy on plasma levels of cortisol. Testosterone was not measured in this experiment. In the second experiment there were 12 intact males and 11 castrated males aged 3 months; six of the lambs in each group were pinealectomized. Prolactin was again greatly stimulated by skeleton long photoperiods and the effect was blocked by pinealectomy; there was a trough in plasma prolactin at dawn in all groups. In addition, castration increased prolactin levels on two of the four sampling days. Plasma cortisol concentrations were significantly lower under skeleton long photoperiods and this was also blocked by pinealectomy; there was no effect of castration. Testosterone was much higher in intact males. After 10 weeks of exposure, skeleton long photoperiods produced significantly lower concentrations than short photoperiods in the intact ram with pineal glands but not in those which were pinealectomized.

Serum Cortisol Levels in Goats Exhibit Seasonal But Not Daily Rhythmicity

“…Several differences between the previous and present study can explain the discrepant results (strain and sex of animals, experimental procedures and conditions). In other ruminant species, seasonal or photoperiodic variation of cortisol levels has also been found in some but not all studies (Brinklow and Forbes, 1984;Bubenik and Brown, 1989;Bubenik et al, 1975;1977;1983;Feher et al, 1994;Ingram et al, 1999;Kennaway et al, 1981;Leining et al, 1980;Lincoln et al, 1982;Monfort et al, 1993). The variability of patterns has been suggested to depend, for example, on the age and sex of the animals or the social structure of the studied herd (Feher et al, 1994).…”

“…Thus, some long-term seasonal variation in cortisol levels might be expected at least in natural conditions, the winter being the period of energy consumption and the summer the period of energy restoration. Indeed, there are studies that have demonstrated annual changes or photoperiodic modulations of glucocorticoid levels, whereas there are also studies which have failed to detect such alterations (Brinklow and Forbes, 1984;Bubenik and Brown, 1989;Bubenik et al, 1975;1977;1983;Feher et al, 1994;Ingram et al, 1999;Kennaway et al, 1981;Leining et al, 1980;Lincoln et al, 1982;Monfort et al, 1993).…”

Comparison of cortisol and rectal temperature circadian rhythms in horses: the role of light/dark cycle and constant darkness

“…In all data points, in both experimental conditions, serum cortisol concentrations were within the physiological range in horses (Kaneko et al 1997). Some authors have reported that cortisol concentrations are influenced by the duration of photoperiod such that long or progressively increasing photoperiods depress serum cortisol, and short or gradually decreasing photoperiods increase cortisol (Leining et al 1980;Brinklow and Forbes 1984). The rhythm did not change between L/D cycle and constant darkness.…”

A Daily Prolactin Rhythm Persists in the Ewe, Foetus and Newborn Lamb After Maternal Pinealectomy in Late Gestation

“…we have confirmed our previous observation of a diurnal fhYthm in maternal and foetal plasma prolactin concentrations In the late pregnant ewe (1) and we have demonstrated that the maternal prolactin rhythm is present until at least 24 h before In the present study there was a rise in maternal prolactin associated with the time of lights off (at 1900 h) in both the intact and pineactomized groups. A number of studies in lambs and sheep have reported that there is a similar 'dusk onset' or 'lights off' peak in prolactin concentrations when the animals are maintained in long photoperiods (11,14,16,18,(20)(21)(22). The neuroendocrine control mechanisms underlying this daily increase in prolactin concentrations are poorly understood.…”