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

The effect of norepinephrine analogue (NA) and norepinephrine antagonists o n luteinizing hormone releasing hormone (LHRH) secretion in geese was inves tigated by monitoring serum levels of LH. Twenty nonlaying geese were selec ted and randomly assigned to 4 groups of 5 each. The geese received a singl e intraventricular injection of saline (control), NA (12 mu g/6 mu l), phen tolamine (1 mu g/6 mu l) plus NA or yohimbine (10 mu g/6 mu l). Phentolamin e, a non-selective adrenoreceptor blocker was given 5 min before NA, but yo himbine, an alpha(2)-adrenoreceptor blocker, was delivered without NA injec tion. The results showed that serum levels of LH began to increase 20 min a fter injection of NA, and that high serum levels of LH were maintained unti l 105 min, followed by a decline to the basal level 125 min later. Signific antly high levels of serum LH were observed at 50 and 105 min after the inj ection as compared with the respective control. Treatment with phentolamine completely blocked the stimulatory effect of NA on serum levels of LH in N A 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 1 25 min later. Five out of 8 points were significantly high as compared with their respective control values. The present study also suggested that the re is presynaptic modulation in the alpha-noradrenergic neural pathways whi ch mediate the release of LHRH, and that this modulation may be carried out by alpha(2)-adrenoreceptor blocker.