Hypothalamic gonadotropin-releasing hormone and pituitary luteinizing hormone contents in the male vole (Microtus agrestis) in the field during the breeding and nonbreeding seasons

Abstract

Pituitary luteinizing hormone (LH) and hypothalamic gonadotropin-releasing hormone (GnRH) contents were measured in male voles trapped in the field over a period of 5 years. Pituitary LH contents were positively correlated with testicular and seminal vesicle weights but hypothalamic GnRH contents showed no correlation with pituitary LH contents or organ weights. Pituitary LH contents and testicular and seminal vesicle weights increased between January to April, reached peak values during May to July, and fell from August to December. Hypothalamic GnRH contents were high for most of the year with low values during December and January. During July, August, and September two populations of males were studied; a group with large active testes and high pituitary LH levels and a group with small testes and low pituitary LH levels. With the exception of the group in July of animals with small testes, all males, both sexually active and inhibited, had high hypothalamic GnRH levels.