A healthy adult subject is given an intravenous injection of a test drug. Both blood pressure and total peripheral resistance rise promptly. This is followed immediately by a reduction of hea rate. In repeated experiments we find that the vasopressor response is not affected by pretreatment with prazosin. However, pretreatment with atropine prevents the cardiac chronotropic response. The test drug was most likely which of the following?

Both BP and peripheral resistance increases , it means drug causes vasoconstriction. Reduction in hea rate is also seen. In repeated experiments we find that the vasopressor response is not affected by pretreatment with prazosin. This means increase in BP is not due to stimulation of a receptor. Pretreatment with atropine prevents the cardiac chronotropic response. It means drug does not have any direct effect on hea rate. So, drug does not act through a receptor and do not have any effect on hea rate. So, the answer would be ANGIOTENSIN II.