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 whether norepinephrine (NE) release in the paraventricular nucleus (PVN) is involved in the glucoprivic suppression of LH secretion in ovariectomized rats. Twelve days after ovariectomy, animals were stereotaxically implanted with a guide cannula for microdialysis in the PVN. Two days later, the PVN was perfused continuously with Ringer's solution or Ringer's solution containing a catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine (100 microM), through a microdialysis probe inserted in the guide cannula 2 h before the beginning of sampling, which lasted 3 h. Blood samples were collected every 6 min through an atrial cannula, 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 concentrations and the frequency of LH pulses decreased. By contrast, when alpha-methyl-p-tyrosine was administered into the PVN, 2DG did not produce 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.