Brain Research, 556 (1991) 157-160 t~) 1991 Elsevier Science Publishers B.V. All rights reserved. 0006-8993/91/$03.50 ADONIS 000689939124766T BRES 24766 157 NG-Monomethyl-,-arginine co-injection attenuates the thermogenic and hyperthermic effects of E2 prostaglandin microinjection into the anterior hypothalamic preoptic area in rats Shimon Amir 1, Emma De Blasio I and Ann M. English 2 1Department of Psychology and 2Departmentof Chemistry and Biochemistry, Concordia University, Montreal, Que. (Canada) (Accepted 30 April 1991) Key words: Prostaglandin E2; L-Arginine; NG-MonomethyI-L-arginine; Nitric oxide; Brown adipose tissue; Thermogenesis; Body temperature; Rat Prostaglandin E 2 (PGE2) microinjection (25 ng, 250 hi) into the preoptic area of the anterior hypothalamus (POAH) stimulated heat production in brown adipose tissue (BAT) and increased core temperature in urethane-anesthetized rats. These thermogenic and hyperthermic effects were attenuated by co-injection of N°-monomethyl-L-arginine(NMMA, 25/~g), a competitive inhibitor of nitric oxide (NO) production from L-arginine. Inclusion of L-arginine (50/zg), though not D-arginine (50/~g) reversed the inhibitory effect of NMMA (25/~g) on intra-POAH PGE2-induced increases in interscapular BAT (IBAT) and core temperatures. Intra-POAH injection of NMMA (25/~g) or L-arginine (50/~g) alone had no effect on IBAT and core temperatures. The results suggest that the effect on thermoregulation induced by action of PGF_~in the POAH is modulated by a local L-arginine-dependent and NMMA-sensitive NO-generating system. Nitric oxide (NO) is an endogenous smooth muscle relaxing factor synthesized from the amino acid L- arginine by the vascular endothelium 5'is. It has been implicated in the regulation of basal vascular tone as well as in the vascular relaxing action of endogenous sub- stances such as acetylcholine and bradykinin 1'21"23. Fur- thermore, NO can be synthesized by peripheral as well as central nervous system (CNS) neurons and has been shown to function as an intercellular messenger or neuromodulator 3-6,l°'11A7"2s'26. Like NO, E prostaglan- dins (PGEs) are potent smooth muscle relaxants in most vascular beds 29. Also, they function as neural messengers or neuromodulators and can exert multiple physiological and behavioral effects in experimental animals 7,12,3°. These include thermoregulatory effects such as stimula- tion of non-shivering thermogenesis in brown adipose tissue (BAT) and powerful hyperthermia 2,s,9,19,27. As part of an investigation of the relationship between central PGEs-induced responses and NO production, we obtained evidence suggesting that NO plays a permissive role in the thermoregulatory action of PGE. Specifically, we found that local treatment with the competitive NO-synthesis inhibitor, NG-monomethyl-L-arginine (NMMA) 2°'22 significantly attenuates the thermogenic and hyperthermic responses to intra-preoptic anterior hypothalamic (POAH) injection of PGE. PGE (PGE2, Sigma) was dissolved in normal saline and microinjected stereotaxically into the POAH of normally-fed urethane-anesthetized rats (275-300 g) pre- pared surgically with thermistor probes for continuous measurement and recording of interscapular BAT (IBAT) and core temperatures as previously described 2. The animals were tested in environmental chambers kept at 22 + 0.5 °C; pre-testing body temperature was kept at 36.5 + 0.3 °C using a thermostatically-controlled heating blanket. Results are shown in Fig. 1 and Table I. An injection of 250 nl of saline containing 25 ng of PGE 2 into the POAH produced a sharp and rapid increase in IBAT temperature which was followed by a smaller and slower increase in core temperature in all animals tested. Inclusion of 25/zg of the NO synthesis inhibitor NMMA (N°-monomethyl-L-arginine, acetate salt, Calbiochem) significantly attenuated the rise in IBAT and core temperatures induced by intra-POAH injection of 25 ng of PGE 2. This inhibitory effect was reversed by the addition of L-arginine (Sigma, 50 /zg), though not o-arginine (Sigma, 50/~g), to the PGE2/NMMA injection solution. Co-injection of L-arginine (50 /tg) did not modify the response to microinjection of PGE 2 (25 ng) into the POAH. Intra-POAH injection of NMMA (25 Correspondence: S. Amir, Department of Psychology,Concordia University, 1455 deMaisonneuve Boulevard West, Montreal, Que. H3G 1M8, Canada.