Kinetics of plasma cyclic GMP and atrial natriuretic peptide after intravenous, intramuscular and subcutaneous injection of 50 micrograms hANP in man.

Plasma kinetics of immunoreactive natriuretic peptide (IR-ANP) and cyclic guanosine monophosphate (cGMP) were studied after intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) application of 50 micrograms human ANP (hANP) in six healthy, male volunteers. The study was single blind. Mean base-line IR-ANP value (N = 54) was 10.8 +/- 1.8 pmol/l. Five min after injection peak IR-ANP concentrations were reached i.v.: 149.5 +/- 94, i.m.: 25.6 +/- 10.8 and s.c.: 18.3 +/- 3.3 pmol/l while cGMP levels reached maximum values at 15 min or 30 min after application: i.v.: 30.6 +/- 12.1, i.m.: 19.2 +/- 8.5 and s.c.: 17.3 +/- 12.3 nmol/l with a mean base-line value of 13.2 +/- 2.1 nmol/l. The calculated corresponding areas under the IR-ANP curves (AUC) achieved about 22% bioavailability for i.m. and s.c. in comparison with the i.v. application. cGMP bioavailability was about 32%. No statistical difference was calculated between i.m. and s.c. application of 50 micrograms hANP. Changes in IR-ANP levels after i.m. and s.c. administration were not accompanied with effects on urine and electrolyte excretion while there was only a tendency in urine volume and sodium increase after i.v. administration. In conclusion after i.m. or s.c. application of hANP only a minor fraction (approximately 1/5) of IR-ANP is available in circulation in comparison with i.v. application with little or no biological effects.