Effects of third ventricle injection of norepinephrine analogue on LH secretion of the non-laying SIJI goose.

Abstract

The effect of norepinephrine analogue (NA) and norepinephrine antagonists on luteinizing hormone releasing hormone (LHRH) secretion in geese was investigated by monitoring serum levels of LH. Twenty non-laying geese were selected and randomly assigned to 4 groups of 5 each. The geese received a single intraventricular injection of saline (control), NA (12 microg/6 microl), phentolamine (1 microg/6l) plus NA or yohimbine (10 microg/6 microl). Phentolamine, a non-selective adrenoreceptor blocker was given 5 min before NA, but yohimbine, an alpha2-adrenoreceptor blocker, was delivered without NA injection. The results showed that serum levels of LH began to increase 20 min after injection of NA, and that high serum levels of LH were maintained until 105 min, followed by a decline to the basal level 125 min later. Significantly high levels of serum LH were observed at 50 and 105 min after the injection as compared with the respective control. Treatment with phentolamine completely blocked the stimulatory effect of NA on serum levels of LH in NA treated geese. Serum levels of LH increased by yohimbine treatment 5 min after the injection and the high levels of serum LH were maintained until 125 min later. Five out of 8 points were significantly high as compared with their respective control values. The present study also suggested that there is presynaptic modulation in the a-noradrenergic neural pathways which mediate the release of LHRH, and that this modulation may be carried out by alpha2-adrenoreceptor blocker.