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<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 < 0.001) to 37.9 ± 2.8 pg/ml. Naloxone also significantly decreased the basal IR-ANF level (P < 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 conciouss 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.
- Atrial natriuretic factor
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