The effects of retinoic acid on the insulin-like growth factor axis in primary tissue culture from hyperparathyroidism.

BACKGROUND: The importance of the IGF system in HPT has been previously demonstrated. Additionally, the role of vitamin A in HPT has been reported. Retinoic acid (RA), a derivative of vitamin A, is a ligand for the IGF II receptor (IGF2R). We have evaluated the interactions of RA with the IGF system in a primary parathyroid cell culture model. MATERIALS AND METHODS: Primary cell cultures were prepared from nine patients. Following adhesion, the cells were transferred to serum-free medium and dosed once with growth factors +/- RA for 96 hours. Proliferation was assessed by measuring tritiated thymidine incorporation. RESULTS: Compared with the control group (100%), both IGF I and II increased DNA synthesis significantly. Retinoic acid significantly reduced the basal DNA synthesis to 82.2% +/- 4.2% compared with control (P < 0.05). Retinoic acid x10(-5) M completely abrogated the proliferative actions of IGF II (70.2% +/- 9.7%, P < 0.05) but had no significant effect on the IGF I response (P > 0.05). To evaluate the role of IGF2R or IGFBPs in mediating the actions of RA, the IGF II analogs [Leu27]IGF II (10-20-fold reduced IGF I receptor affinity) and des(1-6) IGF II (lower IGFBP binding affinity) were used. The IGF II inhibitory effect of RA was enhanced in the presence of analogs [Leu27]IGF II (P = 0.052) but not with des(1-6)IGF II (P > 0.05), compared with wild-type IGF II. CONCLUSIONS: These data implicate a novel antiproliferative role for RA in enhancing the pericellular clearance of IGF II via the IGF2R preventing ligand activation of the IGF I receptor. This may have broader implications for RA effects in other tumors.

Selective estrogen receptor modulators inhibit the effects of insulin-like growth factors in hyperparathyroidism.

BACKGROUND: Primary hyperparathyroidism (HPT) predominantly affects perimenopausal women, leading to speculations that an estrogen imbalance may be liable. We have previously demonstrated the importance of the insulin-like growth factor (IGF) axis in HPT. Because the antiestrogen tamoxifen has been shown to modulate the IGF axis, we examined the interactions of selective estrogen receptor modulators (SERMs) and IGF in HPT. METHODS; Estrogen receptors were evaluated by Western immunoligand blotting. Sixteen parathyroid glands from 19 patients were included. After adhesion, the cells were treated with IGF (I or II) +/- estrogen +/- SERMs (tamoxifen, ICI 182,780) for 96 hours in serum-free media. Proliferation was assessed by measuring tritiated thymidine incorporation. RESULTS: Both primary and secondary HPT express estrogen receptors alpha and beta. Primary and secondary HPT had comparable responses to SERMs, they were analyzed together. Compared with control (100%), IGFs (I and II) induced a significant increase in DNA synthesis. Estradiol at 10(-8) and 10(-7) mol/L (physiologic range) had no significant effects on IGF (I and II, P >.05). Both tamoxifen and ICI 182,780 inhibited basal DNA synthesis (P <.05) and abolished the effects of both IGF I and II (P <.05). CONCLUSIONS: SERMs are capable of reducing basal and IGF-stimulated DNA synthesis. This reduction in proliferation has implications for cancer biology and therapeutic potential for SERMs in HPT.

Efficacy and safety of doxazosin for perioperative management of patients with pheochromocytoma.

Despite adverse side effects, phenoxybenzamine has been widely used for the preoperative management of patients with pheochromocytoma. Doxazosin, a specific a 1-adrenoceptor antagonist, has a pharmacologic profile more suited to controlling blood pressure in such patients. A sequential study of 35 patients with pheochromocytoma encompassed a definite and prescribed change in preoperative drug management from phenoxybenzamine to doxazosin. Hemodynamic, pharmacologic, and biochemical indicators of a- and b-adrenoceptor blockade were measured before, during, and after anesthesia and surgery in 8 patients pretreated with phenoxybenzamine and 27 patients pretreated with doxazosin. Doxazosin (2-16 mg/day) was as effective as phenoxybenzamine in controlling arterial pressure and heart rate before and during surgery, but doxazosin caused fewer undesirable side effects both before and after surgery. Following phenoxybenzamine therapy substantial a 1-adrenoceptor blockade, detected as a right shift of phenylephrine dose-response curves, persisted for more than 2 days postoperatively, whereas after doxazosin it was undetectable on the first postoperative day. Doxazosin provided safe, efficacious pre- and perioperative control of arterial pressure. In patients with predominantly norepinephrine-secreting tumors, pretreatment 24-hour urinary norepinephrine excretion gave an indication of the daily doxazosin requirement.