PARAVENTRICULAR NOREPINEPHRINE RELEASE MEDIATES GLUCOPRIVIC SUPPRESSION OF PULSATILE LUTEINIZING-HORMONE SECRETION

Restriction of glucose availability by 2-deoxyglucose (2DG) suppresses pulsatile LH release. The aim of the present study was to determine w hether norepinephrine (NE) release in the paraventricular nucleus (PVN ) is involved in the glucoprivic suppression of LH secretion in ovarie ctomized rats. Twelve days after ovariectomy, animals were stereotaxic ally implanted with a guide cannula for microdialysis in the PVN. Two days later, the PVN was perfused continuously with Ringer's solution o r Ringer's solution containing a catecholamine synthesis inhibitor, al pha-methyl-p-tyrosine (100 mu M), through a microdialysis probe insert ed in the guide cannula 2 h before the beginning of sampling, which la sted 3 h. Blood samples were collected every 6 min through an atrial c annula, and dialysates were collected every 20 min. One hour after the beginning of sampling, 2DG (400 mg/kg BW) was administered iv through the atrial cannula. Paraventricular NE levels significantly increased immediately after 2DG injection (P < 0.05), and both mean LH concentr ations and the frequency of LH pulses decreased. By contrast, when alp ha-methyl-p-tyrosine was administered into the PVN, 2DG did not produc e an increase in paraventricular NE, and no depression of LH secretion occurred. These results suggest that the PVN mediates the glucoprivic suppression of LH pulses via the release of NE.