Indra Antonipillai

Altered Regulation of Renin Secretion by Insulinlike Growth Factors and Angiotensin II in Diabetic Rats

The etiology of the low renin state in DM is not clear. To assess the role of certain growth and regulatory factors in this process, we studied the effects of insulin, IGF-I, and IGF-II on the renin-angiotensin system in normal and 8-wk STZ-induced diabetic rats. Renin secretion was studied both in static incubations and by perifusion of rat renal cortical slices. In diabetic rats, both plasma renin activity (0.65 ±1.6 vs. 4.0 ±1.2 ng ANG I · ml−1 · h−1) and tissue renin concentrations (27 ± 5 vs. 51 ± 8 ng ANG I · mg tissue−1 · h−1) were reduced. Insulin (0.1–1.0 mu/ml) and IGF-I (10−9 to 4 × 10−9 M) stimulated renin secretion in normal tissue (control, 95 ± 3%; insulin [0.5 mu/ml], 134 ± 7%; IGF-I «4 × 10−9 M], 149 ± 7%). IGF-I stimulated renin secretion in perifusions as early as 30 min, whereas IGF-II had no effect. However, in diabetic renal tissue, neither insulin (0.1–1.0 mu/ml) nor IGF-I (10−9 to 4 × 10−9 M) had an effect on renin. This lack of effect was overcome by adding up to 100-fold higher concentrations of these growth factors. ANG II (10−10M–10−8 M) had an exaggerated inhibitory effect on renin secretion in diabetic tissue. This study suggests that the low renin state in DM may be explained by the enhanced inhibitory effect of ANG II and the resistance to the secretogogue actions of insulin and IGF-I.

Effects of transforming growth factor β and epidermal growth factor on steroid 5α-reductase activity in genital skin fibroblasts ☆

Regulation of steroid 5α-reductase (5αR) activity and dihydrotestosterone (DHT) formation is central to prostate and sexual skin (hair) growth and cell function. Transforming growth factor-β1 (TGF-β1) is a ubiquitous peptide present in skin and scrotal tissue and its receptor is universally expressed. We have explored the role of TGF-β1 and -β2 on androgen formation in skin. Rat or human sexual skin fibroblasts were grown in primary cultures (passage 3–7). 5α-Reductase activity was measured by the %-conversion of tracer 3H-testosterone to dihydrotestosterone over a 4 h period. Incubation of scrotal fibroblasts (2 × 105 cells) in serum and growth factor free media with androgen, such as DHT for two days significantly stimulates 5αR in these cells (1.6-fold, p < 0.05 vs control). TGF-β1 alone at picomolar concentrations (2 × 10−11 M to 2 × 10−10 M) was a potent inducer of 5αR activity in both rat (1.8-fold and 2.8-fold, respectively, p < 0.001 vs control at both doses) and human cells (TGF-β1 2 × 10−10 M 3.3-fold, p< 0.001 vs control). Combined exposure of these fibroblasts to TGF-β1 (2 × 10−10 M) and androgen (10−10 M) further potentiated 5αR activity (rat cells 6.5-fold, human cells 6.4-fold, p< 0.001 vs DHT or TGF-β1 alone). TGF-β2 (2 × 10−10 M), a closely related peptide produced similar effects on 5αR activity in human cells (DHT 1.5-fold, TGF-β2 2-fold, TGF-β2 + DHT 5.5-fold), again synergism was noted with DHT. These effects were not associated with changes in cell number or increased 3H-thymidine incorporation. In contrast, epidermal growth factor (EGF, 5 × 10−9 M) which has a sequence homology with transforming growth factor-α (TGF-α) and interacts with the TGF-α type receptor did not significantly induce basal 5αR or in combination with an androgen. These studies indicate that TGF-β is much more potent than an androgen and is synergistic with androgen in inducing 5αR activity and DHT formation. EGF (TGF-α) has no significant effects on these events. TGF-β may play a role in androgen formation in sexual tissue.

Low dihydrotestosterone and weight loss in the AIDS wasting syndrome

24 consecutive AIDS patients with wasting, and who had never received anabolic therapies, were evaluated to determine their profile of sex hormones and whether transformation of testosterone (T) to the nuclear androgen, dihydrotestosterone (DHT), was impaired. Eleven (46%) patients had normal testosterone and DHT (group I), 10 (42%) had normal testosterone but low DHT (group II), and 3 (12%) had low testosterone and low DHT (group III). Age, prior opportunistic complications, symptoms, serum albumin, hemoglobin levels, and CD4 lymphocyte counts were similar in the groups. DHT was significantly lower (22.2 +/- 6.8 microg/dl) in group II compared with group I (50.8 +/- 15.3 microg/dl). The ratio of T/DHT, a measure of the conversion of testosterone to DHT, in group I was 15.1 +/- 3.5, which was within the range for eugonadal young men. In group II, the ratio was 22.3 +/- 1.5, indicating a defect in generation of DHT. Patients in group II had lost 9.2 +/- 3.5 kg compared with 5.6 +/- 2.6 kg in group I (p = .015). Thus, a syndrome of low DHT with normal testosterone was associated with significantly greater weight loss than in patients with normal testosterone and DHT. Further studies are needed to clarify whether low DHT is a result of AIDS wasting or is causally related to weight loss and whether androgen therapy in the form of DHT could reverse some of the metabolic changes associated with AIDS wasting.

Activin and inhibin have opposite effects on steroid 5α-reductase activity in genital skin fibroblasts☆

The transforming growth factor beta (TGF-beta) superfamily includes several closely related peptides including the activins and inhibins. Since we recently reported that TGF-beta 1 and beta 2 are potent inducers of steroid 5 alpha-reductase (5 alpha R), we have now studied the effects of these other peptides using primary cultures of human scrotal skin fibroblasts. Recombinant human activin A or inhibin A were added to cultured cells (2 x 10(5) cells) for 2 days in a serum free media and 5 alpha R activity was measured by the %-conversion of tracer [3H]-testosterone to dihydrotestosterone (DHT) over a 4-h period. Activin significantly stimulated 5 alpha R activity in a dose related manner (control 3.0 +/- 0.4%, activin (1.2 x 10(-9) M) 6 +/- 0.7%, P < 0.01, (2.4 x 10(-9) M) 8.5 +/- 0.6%, P < 0.001). In comparison, androgen (DHT 10(-7) M) induction of 5 alpha R was 4.7 +/- 0.2%, P < 0.05. Combined exposure of fibroblasts to activin (1.2 x 10(-9) M) and androgen (10(-7) M) did not result in additive or synergistic effect on 5 alpha R activity. In contrast, exposure of cells to an androgen (10(-7) M) and TGF-beta (2 x 10(-10) M) led to synergistic effects on 5 alpha R activity (control 1.5 +/- 0.1%, DHT 2.6 +/- 0.2% TGF-beta 1 4.8 +/- 0.5, TGF-beta 1 + DHT 9.2 +/- 1.2%).(ABSTRACT TRUNCATED AT 250 WORDS)

Renin Response to 12-Hydroxyeicosatetraenoic Acid Is Increased in Diabetic Rats

Eicosanoids (prostaglandins) can alter renin secretion and angiotensin (ANG) II action. We have studied the effects of both prostacyclin and a lipoxygenase (LO) product, 12-hydroxyeicosatetraenoic acid (12-HETE), on renin in normal and streptozotocin-induced diabetic rats. 12-HETE is not only a potent inhibitor of basal renin secretion but also a key mediator of ANG II-induced renin inhibition. We have also examined the effects of ANG II on 12-HETE formation in normal and diabetic animals. Both plasma (3.9 ± 0.9 vs. 0.8 ± 0.1 ng ANG I ç ml−1 + h−1, P < 0.01) and tissue (38 ± 6 vs. 21 ± 2 ng ANG I + mg tissue−1 + h−1, P < 0.05) renin activity levels were markedly reduced in diabetic animals. Iloprost (10−6 mol/l), a stable analog of prostacyclin, had similar stimulatory effects on renin secretion in both normal and diabetic tissues, but the response was enhanced by LO inhibition in diabetic tissue. 12-HETE (10−7 mol/l) had an exaggerated effect on renin inhibition in diabetic tissue (78 ± 2% normal vs. 65 ± 4% diabetic, P < 0.05). Similarly, ANG II (10−8 mol/l) inhibition of renin was significantly enhanced in diabetic rats (P < 0.001). However, ANG II did not produce an exaggerated increase in 12-HETE in diabetic renal tissue. Insulin reversed the inhibitory effects of ANG II on renin in normal rats, but it blunted the effect of ANG II in diabetic rats. These studies suggest that, while the capacity of renal cortical tissue to synthesize 12-HETE in response to ANG II is not altered, 12-HETE and ANG II actions are exaggerated in diabetes, and this may contribute to reduced renin production.

Paracrine regulation of the renin-aldosterone system.

A number of clinical states have been described where there are derangements or discrepancies between renin-angiotensin and aldosterone secretion. We have studied the potential effect of some cytokines or growth factors (peptide regulatory factors) on this system in vitro. Both tumor necrosis factor/cachectin and interleukin I are potent regulators acting as renin secretagogues and inhibitors of aldosterone synthesis. These actions are mediated by prostaglandin cyclooxygenase products and their actions mimic the syndrome of hyperreninemic hypoaldosteronism in critical illness. Insulin and insulin-like growth factor I are also renin secretagogues in vitro However in a diabetic model (streptozotocin rat), there is resistance to both agonists as well as enhanced feedback suppression to angiotensin. A third peptide, transforming growth factor (TGF beta) has even more complex actions, acting as a secretagogue at low doses (10(-12) M) but inhibiting renin at higher doses. TGF beta production is increased in the diabetic state so that this peptide as well as the insulin family may be involved in hyporeninemic hypoaldosteronism.