Effect of Photoperiod and Morphine on Plasma Prolactin Concentrations and Thyrotropin-Releasing Hormone Secretion in the Ewe

Abstract

This study investigated the effects of daily photoperiod length and morphine on thyrotropin-releasing hormone (TRH) and prolactin secretion in sheep. Two groups of adult ewes were kept under either 16hL:8 h D or 8 h L:16 h D photoperiods for approximately 60 days. Then the photoperiods were reversed and approximately 60 days later push-pull cannulae were implanted into the hypothalamic stalk-median eminence. After a 7-day recovery period, the ewes were subjected to hypothalamic perfusion and blood was collected at 15-min intervals from the jugular vein. Perfusates also were collected into 15-min fractions. The first 3 h of perfusion served as an equilibrium period. During the next 2 h, saline was infused into one jugular vein. This was followed by a 2-hour morphine infusion (1 mg·kg^–1 • h^–1). Data from 13 ewes were analyzed for effect of photoperiod and drug on TRH concentrations in the perfusates and prolactin in the serum. Prolactin was significantly (p < 0.01) higher under 16 h L:8 h D than 8 h L:16 h D and was greatly increased (p < 0.001) by morphine infusion. TRH only tended to be higher (p = 0.05) under 16 h L:8 h D than under 8 h L:16 h D, but morphine infusion induced a rapid and highly significant (p < 0.01) increase in TRH secretion. There were no photoperiod and drug interactions for either TRH or prolactin. These results suggest that increased prolactin secretion induced by long-day photoperiods is not mediated by TRH, whereas the morphine-induced increase in prolactin secretion appears to be due at least partially to increased TRH secretion.

The effect of autophagy and mitochondrial fission on Harderian gland is greater than apoptosis in male hamsters during different photoperiods

“…Furthermore, protein expression of ATP synthase and MFF as well as ATP synthase activity was highest in the moderate photoperiod control group. HE staining showed that the HG of striped dwarf hamsters contained a large number of secretory cells of species-specific morphotypes, indicating a possible secretory function, as has been shown in previous studies on female striped dwarf hamsters, golden hamsters, sheep, and other mammals [56][57][58]. Here, we found that after 10 weeks of different light treatment, HG weight in the short and long photoperiod groups was lower than that in the moderate photoperiod group.…”

Photoperiod Affects Harderian Gland Morphology and Secretion in Female Cricetulus barabensis: Autophagy, Apoptosis, and Mitochondria

“…function, as seen in previous studies on rats, sheep, and other mammals (Leshin and Jackson, 1987;Jimenez-Jorge et al, 2007). Similarly, ultrastructural observation of the HG also identified many lipid droplets in the cells, again indicating that the HG may have a secretory function.…”

Effect of Morphine and Naloxone on Plasma Prolactin Concentrations in the Fetal Sheep and Pregnant Ewe during Late Gestation

“…However, Arita and Porter [2] concluded that the decrease in dopamine secretion in duced by morphine in the rat hypothalamus was not suffi cient to account for all of the observed increase in pituitary prolactin secretion. In the adult ewe, morphine infusion was associated with elevated plasma prolactin concentrations and also an increase in TRH secretion from the median emi nence [16]. Previous studies have demonstrated that TRH.…”

“…Thus, acute administration of morphine is associated with fetal and maternal hyperprolactinaemia. Although the endogenous opioids do not appear to mediate basal prolactin secretion in the fetus, they may have a role in the control of prolactin release in the pregnant ewe during late gestation.There is extensive evidence that administration of opioid peptides or opiates can stimulate prolactin secretion in a variety of species including rat, man and sheep [7,16, 24, 25, 30]. As opioid peptides and opiates are unable to stimu late pituitary cells in culture to release prolactin directly, it has been argued that these compounds act via the hypotha lamus to stimulate pituitary prolactin secretion [4, 24].…”

“…Opioid peptides and opiates modulate dopamine release and turnover in the rat median eminence [5,6,11,12, 31, 32] and TRH concentrations in hypothalamic perfusates in crease in parallel with peripheral plasma prolactin concen trations after morphine administration in the sheep [16]. Thus, at least two hypothalamic neurotransmitters, dopa mine and TRH, may mediate the actions of opiates on pro lactin release.…”