The Effects of Temperature Stress on the Bovine Pituitary-Adrenal-Ovarian Axis: An In-Vitro Study.

Abstract

The effect of temperature stress on profiles of LH and FSH from pituitary cells; aldosterone, progesterone, cortisol and corticosterone from adrenocortical cells; and estradiol and progesterone from granulosa cells were evaluated using bovine anterior pituitary, adrenocortical and granulosa cells in primary cultures. Cells were grown to confluency in a 37$\sp\circ$C humidified incubator containing 95% O$\sb2$ and 5% CO$\sb2$. Upon reaching confluency, half of the wells were assigned to 40$\sp\circ$C incubation temperature while the other half remained at 37$\sp\circ$C. The 37$\sp\circ$C temperature represented control conditions whereas 40$\sp\circ$C represented heat stress. Various biological substances, that have been reported to alter hormone production, were added primarily to determine interactions with incubation temperature. The effect of temperature on LH release by unstimulated pituitary cells, after 24 hr at the higher incubation temperature, varied from one of no effect to lower LH secretion. The 40$\sp\circ$C incubation temperature decreased the LH response to GnRH stimulation. Levels of LH stored in the cells were not consistently related to incubation temperatures. LH concentration in the media was lower for $\beta$-endorphin treatment at 40$\sp\circ$C than at 37$\sp\circ$C. This difference was more evident when GNRH and estradiol were added to the media. No FSH was detected in the incubation media with the assay available. Thus, it appears that heat stress decreases the responsiveness of the gonadotrophs to GnRH stimulation. The 40$\sp\circ$C incubation temperature depressed aldosterone production by adrenocortical cells. The effect of temperature on progesterone production varied from one of no effect to an increase at the higher incubation temperature. Cortisol profiles were also varied from one of no effect to an increase or decrease at the higher incubation temperature. Temperature had no effect on corticosterone levels. In the ovarian experiment the profiles of estradiol and progesterone varied from no effect of temperature on estradiol and progesterone secretion, to an increase in estradiol and progesterone secretion at the higher incubation temperature, and to a decreased production of estradiol at the 40$\sp\circ$C temperature.