Effect of cerebroventricular infusion of insulin and (or) glucose on hypothalamic expression of leptin receptor and pituitary secretion of LH in diet-restricted ewes

The objective was to determine the effect of central infusion of insulin an d (or) glucose on hypothalamic expression of leptin receptor and pituitary secretion of LH in the ewe. Twenty-two ovariectomized ewes (32 wk of age) w ere fitted with two lateral cerebroventricular (LCV) cannulae and fed 33% o f NRC requirements for 8 wk. Ewes (n greater than or equal to 5/group) were then infused, via LCV cannulae, with artificial cerebrospinal fluid (aCSF) or aCSF containing physiological concentrations of insulin (INS), glucose (GLU), or INS + GLU; the mass of each increasing linearly from Day 0 (mass = 0 units/h) to Day 8 (mass of INS = 80 mIU/hr and GLU = 10 mg/hr). Jugular serum was collected every 12 min for 4 hr on Days 0, 2, and 4. Ewes treate d with INS or INS + GLU had greater (P < 0.06) mean concentrations of LH th an aCSF treated ewes on Day 2 (13.8 +/- 1.8 and 12.5 +/- 1.3 > 8.0 +/- 3.3 ng/ml). Furthermore, on Day 4, concentrations of LH in INS treated ewes exc eeded that (P < 0.07) of aCSF treated ewes (14.8 +/- 2.0 > 7.4 +/- 3.0 ng/m l). Expression of NPY mRNA did not differ between treatments (P = 0.87), Le ptin receptor mRNA expression was dramatically reduced (P < 0.0002) in INS + GLU versus aCSF treated ewes. These data provide evidence to suggest that insulin may be an important component of hypothalamic mechanisms regulatin g secretion of LH and expression of leptin receptors in undernourished rumi nants. (C) 2000 Elsevier Science Inc. All rights reserved.