The morphine effect on plasma ANF.

The effect of acute morphine treatment on plasma immunoreactive atrial natriuretic factor (IR-ANF) was studied in conscious non-hydrated rats. Morphine treatment induced an 8-fold increase in plasma IR-ANF (P less than 0.001) from 68.1 +/- 9.3 (mean +/- S.E.) to 540.5 +/- 139.5 pg/ml and this increase was completely abolished by pretreatment with the opioid antagonist naloxone (P less than 0.001) to 37.9 +/- 2.8 pg/ml. Naloxone also significantly decreased the basal IR-ANF level (P less than 0.05) to 49.0 +/- 5.3 pg/ml. When naloxone-pretreated and control rats were infused with saline (8 ml) the IR-ANF response was the same in the two groups: 257.7 +/- 64 and 247 +/- 52 pg/ml respectively. Since ANF is a potent natriuretic and diuretic hormone, the morphine-induced increase of plasma IR-ANF may provide a rational basis for explaining the diuretic effect of morphine in conscious non-hydrated rats. Moreover, the decrease of basal plasma IR-ANF suggests the possible implication of endogenous opioids in the regulation of basal ANF secretion.