Stereological studies on the effects of pinealectomy, melatonin and oestradiol on the adrenal cortex of ovariectomised rats.

The aim of the study was to examine by means of stereology the effects of pinealectomy and melatonin on the structure of the adrenal cortex of ovariectomised rats and to check whether the effect of oestradiol on the rat adrenal cortex is modified by the pineal gland. Neither pinealectomy (73 days) nor melatonin treatment (10 micrograms/day for 17 days) changed the absolute and relative weights of adrenal glands of ovariectomised rats or the volumes of individual adrenocortical zones. The average volume of the zona fasiculata cell was higher in pinealectomised than in control rats; adrenal glands of all groups studied contained a similar number of adrenocortical cells. Oestradiol (two injections of estradiol cypionate) resulted within 22 days in a marked increase in adrenal weight, associated with an increase in the total number of parenchymal cells in the cortex of the gland; however, the average volume of adrenocortical cells was unchanged. Neither pinealectomy nor melatonin replacement treatment modified oestradiol effects on the gland. The results cast doubt on the role of the pineal gland and of its principal hormone, melatonin, in influencing adrenocortical structure in the rat and reveal that the pineal gland does not modify oestradiol effects on the gland.