No abstract

Dopamine (DA) and DA agonists bind with high affinity to anterior pituitary receptors which mediate the inhibition of PRL release. Spiperone (SPIP), a DA antagonist, has also been successfully used to characterize pituitary DA receptors with a dissociation constant (Kd) of less than 1 nM. We studied the binding of SPIP to GH3D6 cells which secrete only PRL and GH. This clone was derived from a radiation-induced tumor of the rat anterior pituitary. Equilibrium binding of [3H]SPIP to living GH3 cells showed no high affinity receptors, but a low affinity (Kd = 0.83 microM) and saturable (0.06 fmol/cell) population of sites was observed. In addition, saturable binding with a similar affinity (Kd = 0.57 microM) was noted in broken GH3 cells. The interaction was completely reversible and temperature dependent. The concentration of various ligands required to compete for half of the [3H]SPIP binding to whole cells were: chlorpromazine, 0.17 microM; haloperidol, 0.68 microM; pimozide, 0.77 microM; d-butaclamol, 1.16 microM; 1-butaclamol, 1.30 microM; SPIP, 1.49 microM; bromergocryptine, 4.98 microM; apomorphine, 13.9 microM; and DA, 100 microM. The absence of a high affinity site in GH3 cells is consistent with the decreased effectiveness of various agonists and antagonists on PRL secretion. It is possible that the low affinity interactions observed in GH3 cells are normally present in the anterior pituitary and brain and do not simply represent an alteration of receptor affinity.

Congenital adrenal hyperplasia (CAH) is the most frequent cause of adrenal insufficiency and ambiguous genitalia in newborn children. In contrast to CAH caused by 21 alpha-hydroxylase and 11 beta-hydroxylase deficiencies, which impairs steroid formation in the adrenal exclusively, 17 alpha-hydroxylase/17,20-lyase deficiency impairs steroid biosynthesis in the adrenals and gonads. The sequence of CYP17 gene was determined by direct sequencing of asymmetric PCR products in two French-Canadian 46,XY pseudohermaphrodite siblings suffering from combined 17 alpha-hydroxylase/17,20-lyase deficiency. The two patients are homozygous for the novel missense mutation R96W caused by a C to T transition converting codon Arg96 (CGG) into a Trp (TGG) in exon 1. The both parents are heterozygous for this missense mutation. We assessed the effect of the R96W mutation on 17 alpha-hydroxylase/17,20-lyase activity by analysis of mutant enzyme, generated by site-directed mutagenesis, expressed in COS-1 cells. The presence of R96W substitution almost completely abolished the activity of the mutant protein. The present findings provide a molecular explanation for the signs and symptoms of combined 17 alpha-hydroxylase/17,20-lyase deficiency in these two patients and provide useful information on the structure-activity relationships of the P450c17, enzyme.

This study was designed to evaluate the long-term effect (6 months) of the luteinizing hormone-releasing hormone (LH-RH) agonist buserelin on pituitary and ovarian function in a group of 14 patients presenting with the polycystic ovarian (PCO) syndrome. Buserelin was given subcutaneously 200 micrograms three times daily for the first 7 days followed by 500 micrograms once daily. Blood samples were taken weekly for the first month and then every month for radioimmunoassay of LH, FSH and sex steroids. While LH levels were stimulated during the first 2 weeks and then declined towards baseline, serum FSH levels were reduced after only 1 week (P less than 0.05). Serum oestradiol levels were maximally suppressed to the menopausal range after 1 month and testosterone levels were also significantly inhibited (P less than 0.05) after 2 weeks of therapy. Dehydroepiandrosterone (DHEA) sulphate did not show any significant change while 17-hydroxyprogesterone was suppressed after the first month of buserelin administration (P less than 0.01). The apparent divergent response of the gonadotrophins and the reduction of ovarian steroids in spite of lack of suppression of LH levels can be explained by the marked inhibition of the bioactivity of LH assessed by dispersed mouse Leydig cells assay. The clinical evaluation of hirsutism did not detect any change during the 6 month period. No patient had any menstrual bleeding or spotting after the sixth week of buserelin. The monthly incidence of hot flushes varied between 50 to 66%. This study shows that LH-RH agonist administration can selectively inhibit ovarian function and could be an interesting approach to evaluate the respective contribution of the ovary and adrenal on the pathophysiology of the polycystic ovarian disease. Polycystic ovarian (PCO) syndrome is characterized by tonic and exaggerated secretion of LH leading to an excessive stimulation of the ovarian stroma and an increased production of androgens (Yen et al., 1970; DeVane et al., 1975; Rebar et al., 1976). The androgen precursor delta 4 androstenedione is transformed in peripheral tissues into oestrone (Siiteri & MacDonald, 1973), thus maintaining the state of pituitary hypersensitivity and creating a positive feedback (Yen et al., 1976). The starting point of this vicious circle is still controversial; some argue for a hypothalamic abnormality (Vaitukaitis, 1983) while others support the peripheral origin of the hypersecretion of steroids (Reyniak, 1983). The importance of the adrenal contribution in this syndrome is still unclear.(ABSTRACT TRUNCATED AT 400 WORDS)