Plasma LH levels following electrochemical stimulation of the deafferented medial basal hypothalamus.

Abstract

Abstract. We have investigated the capability of a completely deafferented medial basal hypothalamus (MBH) pituitary complex to support LH release following electrochemical stimulation (ECS) of the arcuate-median eminence (ARC-ME) region. In adult female rats the MBH was completely deafferented (CD) on the morning of pro-oestrus (08.00-10.00 h of day 0). In the first experiment the animals were divided into 5 groups depending on the day of ECS (14.00–16.00 h) and oestradiol benzoate (Oe) treatment (08.00–10.00 h): group No. 1) ECS on day 0; 2) no ECS; 3) ECS on day 1; 4) Oe on day 0 and ECS on day 1; 5) Oe on day 4 and ECS on day 5. Blood samples were collected from the external jugular vein under ether anaesthesia for LH determinations just before and 1 and 2 h after ECS. ECS on day 0 resulted in a significant (P<0.01) rise in plasma LH at 1 and 2 h, while the rats subjected to CD, but not ECS failed to show any changes in plasma LH levels. ECS on days I and 5 (groups 3 and 5) failed to alter plasma LH levels, however, ECS on day 1 in Oe treated rats produced a significant (P < 0.01) elevation in plasma LH that was comparable to that of day 0. In a second experiment Oe was injected on days 1–5 and ECS of the ARC-ME was done bilaterally. ECS on day 5 resulted in a significant (P < 0.05) rise in plasma LH levels in rats with a completely deafferented MBH. In animals with an incomplete deafferentation ECS resulted in a much greater (P < 0.005) rise in plasma LH at l and 2 h. Since LH was released several days after complete hypothalamic deafferentation, these data suggest that LRH secreting cells may be present within the MBH of the rat. In a third experiment injection of LRH (400 ng) on days 0, 1 and 5 with Oe on days 0, 4 or 1–5 resulted in a significant (P < 0.001) rise of plasma LH at 30 and 60 min in all groups. Rats injected on day 0 showed the greatest elevation at 60 min in all groups. Saline injected rats did not show any changes in plasma LH levels.