The actions of histamine on the separated layers of the guinea-pig uterus: the influence of ovarian steroids

Abstract

The effects of histamine have been studied on separated circular and longitudinal myometrial layers from the guinea-pig. Virgin guinea-pigs in dioestrus were (1) untreated, (2) treated for 14 days thrice weekly with oestradiol cypionate 20 micrograms/kg s.c., or (3) treated as in (2) but in addition with progesterone 3 mg/animal s.c. daily for 4 days before use. Preparations were field-stimulated (60 V 2 ms 30 Hz for 5 s every 100 s) to elicit regular contractions. Histamine was equipotent in producing enhancement of evoked contractions of circular myometrium from animals in each treatment group (pD2 = 5.03, 5.05 and 4.95 in groups 1, 2 & 3 respectively), and enhanced contractility in all but two longitudinal myometrial preparations. Treatment with oestradiol alone, and with oestradiol and progesterone following oestradiol priming enhanced the magnitude of maximal response and produced a small decrease in the potency of histamine on the longitudinal myometrium. pA2 estimates for mepyramine as an antagonist were similar (8.6) in preparations of longitudinal myometrium from each group of animals. Metiamide (1-10 mumol/l) did not antagonise the effects of histamine in this layer. These results, taken together, indicate that ovarian steroids act selectively on the longitudinal myometrial layer to amplify the action of histamine, but do not alter the histamine receptor subtype which in this layer is exclusively H1.

Effect of histamine on the longitudinal and circular muscle of the oestrogen dominated rat uterus

“…Although histamine was cquipotent in producing relaxation of the both longitudinal and circular uterine layer (pD2 --4.9 +_ 0.2 and 4.8 _+ 0.1, respectively) the magnitude of the relaxation was significantly larger in the longitudinal muscle. These results agree, at least in part, with those described by Mammen and Pennefather [9] in guinea pig, where histamine produces contraction of both longitudinal and circular uterine layers, and the response achieved by the longitudinal muscle is higher than the circular one. Our results are also similar to those reported by Chow and Marshall [16], since they described a higher response to catecholamines of longitudinal than circular uterine strips isolated from pregnant and non-pregnan t rats.…”

“…Our results are also similar to those reported by Chow and Marshall [16], since they described a higher response to catecholamines of longitudinal than circular uterine strips isolated from pregnant and non-pregnan t rats. Although several explanations have been developed in an attempt to understand this different behaviour between both layers of the animals with a bipartite uterus [1,2,9], our results would support the hypothesis of Anderson et al [8], who suggested that the overall force-generating capacity of the longitudinal muscle is greater than that of the circular layer. It has previously been demonstrated that the histamine H2-receptors in the isolated rat uterus treated with diethylstilboestrol mediate the relaxation elicited by histamine [10][11][12][13][14][15].…”

“…Similarly, it has been described that the longitudinal and circular strips of the uterus of different animal species have different responses to c~-and/% adrenoceptor agonists [3][4][5][6][7], and to inhibitors of prostaglandin synthesis [8], and that these responses may be modulated by ovarian steroids. Mammen and Pennefather [9] have described that histamine usually enhanced the contractility of guinea-pig uterus, but that its potency varies between the two uterine layers. We described that Author for correspondence: I. Martinez-Mir, Departament de Farmacologia, Facultat de Medicina i Odontologia, Universitat de Valencia, Avda.…”