The effect of mestranol and lynoestrenol on uterine histamine in the rat.

Shelesnyak (1959) first suggested that histamine might be the inducing factor for decidualization and that it might be involved in the process of implantation in the rat (Shelesnyak & Kraicer, 1964). Treatment with oestrogen results in histamine depletion from the rat uterus (Szego, 1966; McKercher, Van Orden, Bhatnagar & Burke, 1973), and it was suggested that histamine might be involved in the hyperaemia and oedema stimulated by oestrogen (Szego, 1966). Recently, it has been reported that treatment with the contraceptive steroids, mestranol and lynoestrenol, alone or in combination, resulted in a decrease in histamine content per ovary in the rat (Abdel-Aziz, Ghazal & Daabees, 1974). The present work was undertaken to study the effect of mestranol and lynoestrenol on the histamine content of the rat uterus. Fifty-six virgin female albino rats with a mean body weight of 112 + 5 g were allocated equally to four groups. The animals selected showed regular oestrous cycles. The contraceptive steroids were administered orally and were suspended in 0-5% carboxymethylcellulose (CMC). Treatment was started when the animals were in natural oestrus and was continued for 12 consecutive days, the daily dose being suspended in 0-2 ml CMC. Animals in the first group received 0-08 mg mestranol/rat/day, in the second group 2-5 mg lynoestrenol/rat/day, in the third group 0-08 mg mestranol + 2-5 mg lynoestrenol/ rat/day and in the fourth group corresponding volumes of 0-5% CMC to serve as controls. Histamine extraction was carried out as described by Parrai & West (1957) and histamine bioassay was performed as described by Barsoum & Gaddum (1935). In each group, seven sets of pooled uteri, each from two animals, were extracted for histamine. The uterine histamine content was expressed in terms of^g histamine/g uterus and /uterus. For microscopic examination, histological sections were prepared, and stained with haematoxylin and eosin. Unna's method (1968) was used for differential staining of mast cells. Mast cells were counted per section in the mesometrial triangle, the myometrium and the endometrium. The effect of contraceptive steroids on uterine histamine is shown in Table 1. Treatment with mestranol alone or in combination with lynoestrenol