Rat uterus renin-like activity: effect of stimuli and hormones.

1 The characteristics of renin-like activity in rat uterus were studied. The optimum temperature was 50 degrees C and optimum pH 4.0. Potassium (100 mM) enhanced this activity but sodium or calcium had no effect. 2 Uterine renin-like activity was unchanged 24 h after bilateral nephrectomy. 3 Renin-like activity in the uterus increased slowly from birth to 4 weeks of age and faster between the 4th and 8th week. 4 Ovariectomy caused a considerable fall in uterine renin-like activity. 5 The following factors, known to affect renin secretion in the kidney, i.e., hypovolaemia, sodium loading, adrenalectomy, administration of desoxycorticosterone acetate and injection of isoprenaline, had no effect on uterine renin-like activity. 6 Stilboestrol, an oestrogen, caused a significant increase of uterine renin-like activity. Progesterone and testosterone had no significant effect on this activity but blocked the increase caused by stilboestrol. 7 During pregnancy there was a small but significant fall of renin-like activity in the uterus in the first week and a continuous increase throughout the later period of pregnancy. 8 It is concluded that uterine renin-like activity is independent of kidney renin and does not respond to stimuli affecting kidney renin. Uterine renin activity is hormone-dependent and may be governed by the ratio, oestrogen : progesterone.