J. stcroiclBir&Sr,l. Vol. 16. pp. 403 to 406. 19X2 Printed in Great Bnta~n. All rights rrsorved 0022-473 l/112/030403-04M3.~/0 Copyright 0 1982 Pergamon Press Ltd zyxwvut INFLUENCE OF STARVATION ON THE DIHYDROTESTOSTERONE-LUTEINIZING HORMONE FEEDBA CK IN THE M A LE RAT zyxwvutsrqponmlkjihgfedcbaZ KARL MARTIN PIRKE,JOSE zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF LINO BARAGO*, RICARW CALANDRA?, ISABEL L~THY~ and BARBARA SPYRA Department of Clinical Chemistry, Max-Pianck-institut fir Psychiatric, Kraepeiinstrasse 10. 8000 Miinchen 40. F.R. Germany SUMMARY The suppressing elfect of dihydrotestosterone (DHT) on LH secretion in freshly castrated starved and control rats was studied by impiantin~ DHT releasing silastic capsules of various sizes. Lower plasma levels of DHT are needed to suppress the castration induced LH increase in the starved animals. Intravenous injection of tritiated testosterone (18 PCijlOOg b.wt) revealed a significantly longer hail-life (11.4~ 8.9: P < 0.05) in the starved rat. The ratio [3H]-DHT/[3H]-T in plasma at various times after injection was not significantly different in starved and control animals. The results indicate that the increased sensitivity of tlte f-LH feedback reported earlier [I] cannot be explained by a greater conver- sion T DHT in the starved male rat. I~TROD~lCTlO~ Animufs We recently reported that starvation causes an in- creased sensitivity in the testosterone-leuteinizing hor- mone feedback of the male rat [l]. That means that lower amounts of circulating testosterone are able to suppress the castration induced increase of LH. We had studied the starved rat as an animal model for patients with anorexia nervosa, in whom also, as a consequence of weight loss, the negative feedback: gonadal steroids-gonadotropin is reduced to a pre- pubertal state in male and female patients [l-3]. The nature of the increase in feedback sensitivity is not known. Since DHT is assumed to be the relevant androgen for the hypothalamic and pituitary feedback action (for review see Ref [4]) in the male rat, we studied the DHT-LH feedback. This experiment allows us to test the hypothesis whether an increased T-DHT conversion is responsible for the increased sensitivity of the T-LH feedback observed in the starved rat. Male Wistar rats weighing 200-220 g were obtained from the Central Institute for Laboratory Animals, Hannover. Germany, Altrumin@ rat food and water were available ad ~ib~furnfor the control rats, while starved rats (S) only got water. zyxwvutsrqponmlkjihgfed Half-life oj testosterone in plasma 16 h castrated rats, either fed (C) or starved for 5 days (S) were injected i.v. (through the tail vein) with [3H]-testosterone (18 @/lo0 g b.wt) dissolved in eth- anol-saline (I : 10, v/v) under light ether anaesthesia. Animals were sacrificed by decapitation after 7, 15, 30, 60 or 120 min. Serum was stored at - 3oCC until ana- lyzed. 31ATERlALS AND METHODS Testosterone 1, 1. 6. 7-‘H (81) SA 93.9 Ci/mmol, testosterone 4-lJC SA 57.5 m Cijmmol and dihydro- testosterone 4-“C SA 57.5 mCi/mmol were obtained from New England Nuclear. Dreieckenhain, Ger- many. The put%\ of the tracers was checked by thin layer chromatography. Following the addition of known amounts of [“Cl-testosterone (2~c.~;rn.) and [14C]dihydrotes- tosterone (2000 c.p.m.) and nan-radioactive standards (2 mg each), 500 ~1 of the serum were extracted with 6ml of diethyl ether. One hundred ml aliquots of these extracts were taken for counting. The dried extracts were chromatographed ofi. thin layer plates (silica gel) in the system chloroform-diethyl ether, 4: 1,. The zones corresponding to testosterone (T) and dihydrotestosterone (DHT) were scraped off, eluted with benzene-methanol (2: If and counted. The identi- fication of testosterone and dihydrotestosterone was assessed by constant 3H/‘4C ratios after chroma- tography in three different systems. DH T-4.W feedback * Present address: National institute of Child Health and Human Dc\elopment. National Institutes of Health. Bethesda. Maryland 20014. U.S.A. * insrituto de Bioiogia y Medicina Experimental. Buenos Aires. Argentina. 100 rats were castrated under ether anaesthesia and implanted with silastic tubes which were either empty or filled with DHT. These capsules release steroids at a constant rate [S]. Details of the technique have 403