Development of the sex difference in blood pressure of the chick.

Abstract

In order to establish the age and manner in which the sex difference in blood pressure of the adult white leghorn chicken develops, periodical blood pressure measurements were made on chicks between 3 and 34 weeks of age. There were no consistent differences in pressure between the sexes under 8 weeks of age. Between the 8th and 13th weeks, pressures began to diverge, and within 4–8 weeks a 26–30-mm sex difference in systolic pressure developed. Significant divergences occurred also in diastolic and pulse pressure. The sex divergence was due primarily to a rise in male pressure, the female level remaining comparatively stable. Net changes in male parameters during the period of rapid development of the sex difference in pressure were: body weight + 219 gm, systolic pressure + 26 mm, diastolic pressure + 16 mm and heart rate –22/ min. The age at which the sex difference in pressure begins and its rate of development appear to be related to sexual maturation in the male. However, no significant correlation between the rising male pressure and testes or comb size could be shown. Normal chick blood pressure values prior to the sex divergence differ within strains of white leghorns and for the two groups used here, between 7 and 9 weeks of age, were 150/130 and 162/136 mm Hg.