Serum neurophysins during passive assumption of the erect posture in men and during pregnancy: effect of syncope.

A slight but reproducible increase in serum total immunoreactive neurophysin levels (IRN) occurred 30 minutes following passive assumption of the erect posture (tilt test) in 12 men (17%, 2 P is less than .02) and in 6 pregnant women (20%, 2P=NS) who showed normal cardiovascular adaptation during the test and did not suffer syncope. The increase was much more marked in 4 men in whom there was a fall in blood pressure and syncope in assuming the upright posture. An increase of twice the basal level was also found in a pregnant women who experienced syncope, although she was maintained horizontal. Our results show that it is important to ensure the absence of these intercurrent phenomena in the correct interpretation of dynamic clinical tests of neurohypophysial function.