Alteration in the relationship between tanycytes and gonadotropin releasing hormone (GnRH) neurosecretory terminals following long-term metabolic manipulation in the sheep

Abstract

The activity of the hypothalamo-pituitary gonadal (HPG) axis is influenced by energy reserves, such that an increase or a decrease in adiposity may perturb the secretion and action of GnRH. This is thought to be due to the signalling of hormones such as leptin, which act upon neuronal systems controlling GnRH secretion. Other work shows plasticity in the relationship between tanycytes and GnRH neurosecretory terminals in the median eminence across the estrous cycle and we hypothesised that similar plasticity may occur with altered metabolic status. We studied Lean, Normal and Fat ovariectomised ewes, which displayed differences in gonadotropin status and investigated the relationship between tanycytes and GnRH neuroterminals. In both Lean and Fat conditions, altered anatomical arrangement between these two elements was observed in the vicinity of the blood vessels of the primary plexus of the hypophysial portal blood system. These data suggest that such plasticity is an important determinant of the rate of secretion of GnRH in animals of differing metabolic status and this contributes to the relative hypogonadotropic condition that prevails with metabolic extremes.

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