A renin-like enzyme in rat luteal tissue: evidence of local synthesis and its regulation during pregnancy.

Changes in the concentration of a renin-like enzyme were studied in androgenized rats in which a single luteal phase was induced by the administration of chorionic gonadotrophin. A significant increase in the luteal renin-like enzyme (RLE) concentration was found between the youngest corpora lutea (48 h old) and the oldest one studied (6 days old). The luteal RLE content varied independently of changes in plasma renin concentration. These results suggest that this enzyme was produced locally. The lack of correlation between the luteal RLE and plasma prolactin supports our previous observation that the changes in luteal renin concentration appear not to be prolactin-dependent. Furthermore, the suckling-associated hormones appear not to be related with the regulation of luteal RLE concentration, since the values were not modified in androgenized maternal rats which were suckling when compared with the controls. Changes in luteal renin concentration were also studied during pregnancy. A significant increase was found a few hours after a fertile mating which reached a peak on day 1 of pregnancy, followed by a rapid decrease to low levels throughout the remainder of the pregnancy. Because the renin-angiotensin facilitates angiogenesis, luteal renin may act as an angiogenic factor, stimulating blood vessel growth in the corpora lutea. An alternative hypothesis is that the increase in RLE could be a trigger for calcium flux redistribution and steroid biosynthesis.

Cyclical changes in plasma renin during the oestrous cycle in the rat: synchronized effect of oestrogen and progesterone.

The aim of the present work was to study the relationship between sex hormones and plasma renin levels during the oestrous cycle in a Wistar-derived rat strain. Plasma renin activity (PRA) as well as a plasma renin concentration (PRC) were increased during the day of oestrus in rats with controlled 4-day oestrous cycles. This increase in PRA and PRC was not found when rats were ovariectomized on dioestrus day 2 and samples measured on the expected day of oestrus. The increase in PRA and PRC was not found when normal cyclic rats were treated with either tamoxifen or the progesterone receptor blocker RU 38486. Treatment with progesterone at pro-oestrus after ovariectomy on dioestrus day 2 partially increased the PRA and PRC when compared with the values found during the day of oestrus in control rats. The combined treatment of ovariectomized rats on dioestrus day 2 with oestrogen and progesterone restored the normal increase in PRA and PRC values on the expected day of oestrus. We therefore postulate that the sodium diuresis promoted by progesterone may be modulated by the previous peak of oestrogen. However, stimulation of extrarenal sources of renin cannot be excluded nor can an involvement of inactive precursors of renin in the fluctuations of active renin that occur during the oestrous cycle. No important change in plasma renin substrate (PRC) was observed during the oestrous cycle. PRA, PRC and PRS were determined every 4 h during the 4-day oestrous cycle. Our results clearly show a rhythmic variation in PRA and PRC which increases during the day of oestrus with a peak at 06.00 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes during lactation in the renin-like enzyme concentration in rat luteal tissue.

The activity of a renin-like enzyme (RLE) previously found in rat copora lutea was studied during lactation. Luteal RLE concentration significantly increased after delivery and reached a maximum on day 5 of lactation. Plasmatic levels of PRL and progesterone also increased through lactation. Treatment with 2 bromo-alpha-ergocryptine, which diminished plasma PRL and progesterone levels, enhanced luteal RLE activity. Therefore, the increase in luteal RLE during lactation seems to be independent of PRL and progesterone levels, but dopamine could be involved in its regulation. The increase in luteal RLE is not related to the intensity of the suckling stimulus, since RLE values were not modified in mothers suckling 2 to 10 pups. In conclusion, RLE activity in rat corpora lutea changes during lactation with a pattern similar to that of plasmatic PRL and progesterone, but seems not to be regulated by these hormones, nor by the intensity of suckling. On the contrary, luteal RLE may be regulated by dopamine.

A renin-like enzyme in luteal tissue.

The aim of this study was to identify immunologically and biologically a renin-like enzyme (RLE) in rat corpora lutea (CL). The biological activity of partially purified extracts of CL was tested in vivo by injection into anesthetized pentolinium-treated rats, obtaining a pressor response similar to renal renin. The enzyme activity in vitro was inhibited to about 50% by pretreatment with a specific antibody against renal renin. When the extracts were incubated with angiotensinogen, the product was inhibited mainly by angiotensin I antibody. The fact that there was no change in RLE content in 24 or 48 h nephrectomized rats, suggested the idea of a local production rather than an active blood renin sequestration.

Half-life of circulating renin under different experimental conditions.

The half-life of circulating renin was studied in normal rats and in rats with a single kidney that was ischemic. The resulting disappearance curve represented the sum of two exponentials. The average half-life of the fast component was 11.5 minutes for normal rats, 11 minutes for rats with mild renal ischemia, and 8 minutes for rats with severe renal ischemia. The mean half-life of the slow component was 67 minutes in normality, 84 minutes in mild ischemia, and 121 minutes in severe ischemia. Also, the calculated proportion of the slower component was different for each group--60.3% in normality, 68.2% in mild ischemia, and 82.2% in severe iischemia. The results suggest that more than one kind of renin may be produced and released by the kidney, and also that renal ischemia may modify the normal metabolism of renin.