Most studies examining the developmental aspects of renin secretion in fetal lambs have focused on measurements of active renin. Data from these studies demonstrated age-dependent differences in renin release in vivo and in vitro. However, little information is available concerning gestational changes in total (active and inactive) renin. Therefore, we have measured the renin concentration in plasma, amniotic fluid and various tissues before and after trypsin treatment (for total renin) using 7 fetuses at 0.61–0.79 gestation (immature) and 7 fetuses at 0.88–0.97 gestation (mature). We found that active and total renin levels in plasma and kidney tissues were significantly lower in immature than in mature fetuses, while inactive renin levels were not different. We also found that the amniotic fluid, the adrenal gland, the placenta and membranes all contained low levels of active and total renin that were not different between groups. These results suggest that, over the last third of gestation, maturation influences the regulation of active renin in the kidney and plasma. The data also indicate that the renin concentration in the amniotic fluid, the adrenals, the placenta and membranes is regulated differently than that in the plasma and the kidney.

Brain-derived neurotrophic factor (BDNF), at doses of 0.04, 0.4 or 4.0 microg/day, was delivered by cannula and s.c osmotic minipump into the ipsilateral vestibular nucleus complex from 0 to 50 h following unilateral labyrinthectomy (UL) in guinea pigs. Compared to the vehicle control group, the frequency of spontaneous nystagmus was significantly reduced (p < 0.02) and the rate of yaw head tilt compensation increased (p < 0.02). However, roll head tilt was not signifcantly affected. There were also no significant effects of BDNF administration into the IVth ventricle (4.0 microg/day) on any UL symptom. These results further support the hypothesis that neurotrophins such as BDNF may enhance the vestibular compensation process.

We studied the content and secretion of renin by renal cortical slices obtained from ovine fetuses at 0.62-0.77 gestation (n = 5 immature) and at 0.84-1.00 gestation (n = 5 mature). Renin content of fresh slices and renin secretion after the incubation of slices in Robinson's medium with or without isoproterenol or dibutyryl (DB) adenosine 3',5'-cyclic monophosphate (cAMP) (10(-4)-10(-8) M) were measured. Renin content of immature fetal kidneys (ng.ml homogenate-1.h-1.mg-1) and basal renin secretion rate [ng (ANG I/h).mg tissue-1.h incubation-1] were 24.3 +/- 3.0 and 1.4 +/- 0.4, respectively. Both of these values were significantly lower (P less than 0.02) than the corresponding results obtained with mature fetal kidneys (67.0 +/- 4.5 and 3.4 +/- 0.5). Renin content and basal secretion rates were strongly correlated (r = 0.78, P less than 0.01). The addition of isoproterenol or DBcAMP induced a significant increase in renin secretion only when incubated with slices from mature fetuses. We conclude that there is a deficit in the beta-adrenoceptor-mediated renin release distal to cAMP formation in immature fetuses, which may be related to low renal content of renin at this stage of development.

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