[Release mechanisms of inactive renin from rat renal cortical slices: role of the submandibular gland].

In our previous studies, we showed an in vivo stimulating effect of the extract of the rat submandibular gland on plasma inactive renin release. In this study, we evaluated the effects of the rat submandibular gland extract and of some plasma active renin stimulants on inactive renin release from rat renal cortical slices. Adult male Wistar rats (250-350g) were kept on a regular diet (Na 260mg/100g) and nephrectomized under pentobarbital anesthesia (50mg/kg, i.p.). Five thin renal cortical slices were obtained from each kidney by using a razor blade. These renal cortical slices were incubated in Earle's buffer (pH7.4, Difco) at 37 degrees C for 30 min (preincubation), then transferred into 10ml fresh Earle's buffer with or without some agents and incubated at 37 degrees C for 1 hour (experimental incubation). For each experiment, 6 groups of 5 renal cortical slices were employed. The agents used in this study were as follows: isoproterenol (10(-5)M), furosemide (50 micrograms/ml), prostaglandin E1 (10(-5)M), prostaglandin I2 (10(-5)M) and the rat submandibular gland extract (100 microliters) which was obtained after homogenation with 10 x (w/v) 0.01M pyrophosphate buffer (pH6.5) including 0.1M NaCl. One ml of samples of this Earle's buffer were withdrawn every 20 min. Active renin in the samples was assayed by the commercial RIA-kit (Dainabot), and total renin was assayed after trypsin (Worthington) treatment (30 micrograms/300 microliters sample) at 4 degrees C for 10 min. Inactive renin was determined as the difference between total renin and active renin. Active and inactive renins increased linearly in the buffer without any agents (control) during the observation period (60 min). Isoproterenol (10(-5)M) stimulated the release of active renin significantly (p less than 0.01 vs. control) but did not affect the release of inactive renin. Furosemide (50 micrograms/ml) stimulated the release of active and inactive renins significantly at 20 and 40 min (p less than 0.05 vs. control) but did not affect the release of either renin at 60 min. Both prostaglandins E1 and I2 (10(-5)M) stimulated the release of active renin significantly (p less than 0.01 vs. control) but inhibited, on the other hand, the release of inactive renin significantly (p less than 0.01 vs. control). The rat submandibular gland extract (100 microliters) did not affect the release of active renin but stimulated the release of inactive renin significantly (p less than 0.05 vs. control).(ABSTRACT TRUNCATED AT 400 WORDS)