17beta-Hydroxy-C19-steroid dehydrogenases from male guinea pig liver. Purification and characterization

One major and six minor 17beta-hydroxy-C19-steroid dehydrogenases were isolated each in a highly pure form from male adult guinea pig liver by a combination of gel filtration and ion exchange chromatography. Molecular weight, amino acid composition, sugar content, number of sulfhydryl groups. NH2-terminal amino acid, isoelectric point, substrate specificity, pH optima, Km values, and inhibitory effect of other steroids were studied. The amino acid composition, Km values, and substrate specificity indicated two separate groups of enzymes. The first group possessed a dual coenzyme requirement and specificity for 5beta-androstanes, whereas the second group showed apparent TPN+ and 5alpha-androstane specificities. Phosphate enhanced the DPN+-related activity of the first group and evoked DPN+-linked activity in the second group of enzymes. A molecular weight of 31,000 to 32,000 with a single chain structure was estimated for four of the enzymes. The other three enzymes consisted of two components of 24,000 and 11,000 daltons.     

Ontogeny of androgen receptors in fetal guinea pig brain

Sexual differentiation of the guinea pig brain is androgen dependent. To understand the cellular mechanisms of androgen action, we studied the ontogeny of cytosolic (ARc) and nuclear (ARn) androgen receptors in the brains and anterior pituitaries of fetal, neonatal, and adult guinea pigs. Using cytosol from the hypothalamus-preoptic area-amygdala-septum of 60- to 65-day fetuses and nuclear preparations from 6-day-old neonates treated with testosterone propionate, validation studies revealed an AR with an apparent Kd of 1.9 +/- 1.1 (mean +/- SEM, n = 3) x 10(-10) M (ARc) and 3.4 +/- 3.2 (n = 3) x 10(-10) M (ARn). The cytosolic receptors were highly specific for androgens. After assay validation, AR content was determined from specific brain regions of fetuses obtained on Days 30, 40, 50, and 59 of gestation and on Days 6 and 120 postpartum. ARc differed significantly (p less than 0.05) between brain regions and times of gestation, but no sex differences were apparent. In contrast, ARn showed little difference between tissues or with gestational age, but there were significant differences between males and females, especially in late gestation and early postnatal life, with males having greater ARn binding (p less than 0.05). These data demonstrate the presence of ARc and ARn in the fetal brain and pituitary gland during the critical period of sexual differentiation (Days 30-37 of gestation), thus establishing the identity of cellular structures involved in androgen action.     

Effects of exogenous steroids on androgen receptors in fetal guinea pig brain

We treated pregnant guinea pigs on Day 50 of gestation with 10 mg testosterone propionate (TP), obtaining fetuses 2, 4, 8, or 18 h later as well as after 5 days of treatment. In a second group of pregnant guinea pigs, dihydrotestosterone propionate (DHTP), estradiol benzoate (E2B), progesterone (P), or cortisol was given 2 h before obtaining fetuses. Although TP treatment elevated fetal serum T (p less than 0.05), brain cytosolic androgen receptor (ARc) content was unchanged in fetuses of either sex. In female fetuses, nuclear androgen receptors (ARn) increased 10-fold in medial-basal hypothalamus (MBH) and preoptic area (POA) at 2 and 4 h (respectively) after treatment, while fetal male ARn content was unchanged. Maternal injection of other steroids (E2B, P, or cortisol, but not DHTP) significantly increased these hormones in the fetus 2 h later (p less than 0.05). Only androgens affected fetal androgen receptor (AR) content. While TP increased ARn in female MBH, DHTP decreased ARc in fetal anterior pituitary of both sexes. In this latter case, a metabolite of DHT may mediate the effects. We conclude that T crosses the guinea pig placenta and activates ARn in POA and MBH of female fetuses; male ARn appear to be maximally occupied by endogenous T. Steroids of other classes do not induce AR responses in fetal guinea pig brain. These AR changes may represent an initial cellular mechanism in brain sexual differentiation.     

Mechanogram profile of the guinea pig intestine. The supertone

The authors detected the possibility, during the phase of low tone contraction of isolated intestine, to develop a further contraction, a supertone (S), simply washing the preparation. It has been evidenced that S appears when the tonic phase is low; it does not disappear if the tone is increased lowering NaCl concentration in the saline plasma; is absent in the KCl induced contraction; is induced also by low doses of atropine; is decreased by digitalic agents. The results obtained lead the authors to conclude that: the reduced tonic phase is due to a positive factor, the Ca++ of the cytoplasm, and to a negative factor, the high level of cytoplasmic Na+. This high level of Na+ is maintained by a dynamic equilibrium with ion input through channels opened by muscarinic agent and output by a Na-K-ATP asi pump. The Na+ output is predominant and fraction of Ca++, no longer counterbalanced by Na+, causes the rise of S.