Vaginal Potential in Estrous Cycle of Rats

Bruzzone ME, Angelo S, Zipperj, Wheeler RG (Dept of Biophysics and Physiology, School of Medicine, University of Chile, Santiago, Chile, and the International Fertility Research Program, Research Triangle Park, NC, USA). Endocrinologic basis of electrochemicalcoginalpotential in estrous cycle of rats. IntJ Gynaecol Obstet 18. 22-25, 1980 This sequel to an earlier report on the correlation of vagino-oral voltage measurements in rats with their estrous cycles deals with the endocrinologicactivation of these volt­ ages. The normally sinusoidalvoltages, positive duringestrus and negative during diestrus, were absent in spayed rats but were restoredwith a single intraperitonealinjection of 5 /ig or more of 17,R-estradio/ or with 0.1 mg of adrenaline iniectedsubcutaneous1,ev.y12 hours. Estrogen antagonists, drugs that inhibit catecholamine synthesis or adrenergic P3 blockers, totally inhibit the negativepotentialrecordedduring estrus. Vaginal estrous potentials in the rat reflect an important reproductivestate ',,vsibly linked to sexualbehavior (heat) or to ovulation. Triggering of the cyclic potential by adrenalinewithout estrogenicmedicationsuggests that adrenaline belongs to the group of sexual-specific hormones. INTRODUCTION The variations ofelectropotentials associated with the reproductive functions have been studied since the initial works of Burr in 1935 (2, 2P 3). No cyclic variations in any of the species studied (4, 7) were reported, however, until the work of Zipper and Angelo (12), who measured vagino-oral potentials in rats. Using KCI electrodes, Zipper and Angelo observed negative vaginal potentials during estrus that became positive during diestrus. In spayed animals, the positive potential became permanent. This potential is also positive throughout the gestational period in rats, becoming ncgotire the first day after delivery. These observations led us to study the possibility of an endocrinologic origin of these cyclic estrous potentials. The most important hormones offering cyclic variations in concentration during the estrous cycle in the genital tract of the rat are I7fl-estradiol, progesterone and epinephrine (10). Other hormones and some inhibiting agents of the action of cate­ cholamines were also studied. MATERIALS AND METHODS Female rats of the Sprague-Dawley strain were used, weighing 200 gm-250 gin. The rats were spayed 15 days before potentials were measured. Measurement of voltages was performed under tri­ bromethanol anesthesia (Avertin, Winthrop Labo­ ratorics, New York, NY, USA). The ability to con­ sistently measure changes in potential with the es­ trous cycle 'ndicates that the anesthetic does not obscure potentials. Nonpolarizable electrodes were made of three molar KCI in 2% agar, inside polyethylene tubes with an inner diameter of 0.85 mm and an outer diameter of 1.25 mm. This KCI electrode was con­ nected through a 3 M KCI solution to a silver wire anodized in HCI. New electrodes were prepared for ea.ch measurement, and the system was checked for polarization in an NaCI solution each time before use. Voltage measurements were obtained with a dual beam Tektronix 502 oscilloscope. The positive elec­ trode was placed in the vagina and the negative one on the tongue (vagino-oral potentials). Twenty groups of 4-8 animals were formed. Voltage mea­ surements were performed daily at 10 a.m. The hormones and chemicals used were bought at the Sigma Laboratories. The drug regimens used on 20 IntJ Gynaecol Obstet 18 experimental groups of animals are shown in Table T. RESULTS On each of the voltage-versus-time graphs (Figs. 1-6.), the average standard deviation of voltage for the plutted points is indicated by the length of the Table I. Drug regimen used on 20 groups of 4-8 animals. . . ... . .... .. i n.-, n:,t No . . . . . .17 -est,Odn uTruio u 2' 3 41 IA 1 16'_f : 5,gfOmag , Irtl~ l monle X0.l (one (one inlrap rfoOnea+nier, ) mg.,(ne ........................... Adrenaline .02 mg Iwo 0 sbCutamnoas reectons of ? 0 .0? ..... ou..... of O nmq eery 12 hour) 02 mg {JayIone st)cutaneot-ollemtor I of 0 I gnerir 12h.o for eght day, Progeewcn. 11:,q(orne iraperltoneal orl Noradmenal ne .0 001f lg tone tubO,fanoa ,fnc onE. r dailyng Itiraldreto al X I Propranolol .10 mg kq(ay one ntrapewtoneal XI 1f0mg k day (0ne,ntraptritoneal . injectiondailyl 96 hour, before r,,t,atonof other treatet Fg'eno