Testosterone and dihydrotestosterone content of the testis during guinea pig]

The fetal guinea-pig testis synthetizes testosterone and reduces it in 5 alpha-dihydrotestosterone. The embryonic period which goes from the gonadla differentiation (on day 23) up to the beginning of the sex ducts differentiation (on day 29) is characterized in male guinea-pig by a very important testicular load in testosterone and DHT.     

Simultaneous radioimmunoassay of testosterone and dihydrotestosterone

A radioimmunoassay, which simultaneously measures both testosterone (T) and dihydrotestosterone (DHT) in the same serum sample, is presented. Celite column chromatography is employed to separate T from DHT, and these two steroids from other potentially cross-reacting and interfering steroids. The normal values for men, women in the follicular phase, women in the luteal phase, ovariectomized and adrenal ectomized women, post-menopausal women and ovariectomized women for T are 5, 140 ± 1190 pg/ml, 307 ± 97 pg/ml, 285 ± 46 pg/ml, undetectable (<5 pg/ml), 262 ±47 pg/ml and 199 ±44 pg/ml; and for DHT 470 ± 165 pg/ml, 160 ±45 pg/ml, 147 ±44 pg/ml, undetectable (<5 pg/ml), 168 ± 27 pg/ml, 94 ± 15 pg/ml. The maximum sensitivity of the method was 10 pg/ml for T and 14.3 pg/ml for DHT when 1 ml was extracted. The blank in most assays was undetectable, but rarely exceeded 10 pg.     

Inhibition of testosterone metabolism in cultured rat epididymal principal cells by dihydrotestosterone and progesterone

To evaluate the effects of steroids entering the epididymis in rete testis fluid on testosterone (T) metabolism by the epididymal epithelium, principal cells were isolated from the proximal caput, distal caput or corpus epididymidis by enzymatic dissociation and elutriation and were cultured at 34 degrees C within a floating collagen matrix. The culture medium was supplemented with T, dihydrotestosterone (DHT), T plus estradiol-17 beta (T + E) or T plus progesterone (T + P) at concentrations which were approximately physiologic. Metabolism of T by principal cells incubated for 2.5 days with DHT was lower (P less than 0.05) than for control cells cultured with T. Inclusion of E or P in the culture medium lowered (P less than 0.05) metabolism of T by principal cells from each region. However, principal cells cultured with T + P for 2.5 days and then washed and cultured for 12 h with T alone, metabolized T as well (P less than 0.05) as cells never exposed to P. In marked contrast to the persistent suppressive effect of DHT, the suppressive effect of P on metabolism of T is rapid, direct and rapidly reversible. Thus, metabolism of T by principal cells in the epididymal epithelium may be modulated by steroids (E + P) in rete testis fluid or by steroids (DHT) produced locally in the epididymis.     

The metabolism of testosterone and dihydrotestosterone in an androgen-dependent tumour. A possible correlation between dihydrotestosterone and tumour growth in vivo

The effects of dihydrotestosterone (17beta-hydroxy-5alpha-androstan-3-one) and testosterone on the growth of the androgen-dependent Shionogi SC-115 tumour in mice have been compared and the metabolites in the tumour arising from each steroid have been identified. After the transfer of SC-115 tumour cells to castrated male mice, treatment of the recipients with dihydrotestosterone produced a striking proliferative response that enabled earlier tumour detection and led to a higher tumour incidence than obtained with testosterone. At short intervals after the intravenous injection of 200muCi of [1,2-(3)H]testosterone the amounts of radioactivity in tumour, muscle and seminal vesicles were almost equal. The metabolism of [1,2-(3)H]testosterone in tumour and muscle was slight in comparison with the extensive metabolism in seminal vesciles. Whereas up to 7% of the total neutral steroid recovered from whole tumour tissue and isolated nuclei was in the form of [1,2-(3)H]dihydrotestosterone, the amount of this compound in the corresponding preparations from seminal vesciles was several times greater. When the metabolism of [1,2-(3)H]dihydrotestosterone in tumour tissue was studied, it was found that more than 60% of the total neutral steroid in both cytoplasm and nuclei consisted of [1,2-(3)H]dihydrotestosterone. Thus much higher intracellular concentrations of dihydrotestosterone occurred with the administration of this steroid than with testosterone. Tumour cell proliferation was suppressed by oestradiol and the amount of androgen in nuclei was significantly decreased by high doses of this hormone.     

Ascorbic acid uptake in guinea pig intestinal mucosa

Cellular accumulation of ascorbic acid was investigated in vitro in distal intestinal mucosa of guinea pig. With ¹⁴C-ascorbic acid present at 8 μM/L in the bathing media, tissue/media (T/M) concentration ratios of at least 5 were routinely achieved. Recently absorbed ascorbic acid appeared to be free in solution in the cellular fluid in that it diffused from tissue exposed to poisons with a disappearance half-time of approximately 10 minutes. Ascorbic acid uptake was highly dependent on the presence of sodium in the bathing media; total Tris substitution resulted in a 97% decrease in uptake. Also, metabolically depleted tissue did not accumulate ascorbic acid against a concentration gradient. Uptake of ¹⁴C-ascorbic acid from a bathing solution concentration of 8 μM/L was reduced 67% in the presence of 0.8 mM/L nonlabeled ascorbic acid. Recently absorbed ¹⁴C-ascorbic acid moved more rapidly back into the lumen when the luminal solution contained nonlabeled ascorbic acid (5 mM) than when it contained mannitol (5mM). This demonstration of counter transport substantiates a carrier mechanism in the brush border.     

Iron metabolism and placental iron transfer in the guinea pig

The interrelationship between fetal iron uptake and maternal iron metabolism has been studied in the guinea pig in the course of pregnancy. The rapid increase of the maternal need for iron during the period of fast increasing rates of placental iron transfer is largely compensated for by increased intestinal absorption. No enhanced mobilisation of iron from the liver and spleen iron stores could be demonstrated. The plasma iron turnover, corrected for the transplacental iron transfer rate, remained constant during pregnancy. This means that not only the mobilisation of iron from the stores remains principally unchanged, but also the supply of iron to the maternal organs and tissues. The haemoglobin concentration decreased by about 15% during the period of rapid fetal growth and iron uptake. The maternal blood volume increased during this very period and explained most of the observed reduction. Intestinal iron absorption increases. At day 55 of pregnancy placental iron transfer is maximal. It could be shown that a day 55 the rate of intestinal iron uptake equals the rate of iron transfer across the placentas. It is evident that pregnancy effects a direct influence on intestinal iron absorption, independent of the magnitude of the maternal iron stores. How this influence is realized without changing the iron kinetics of the maternal stores, cannot be explained with the prevailing theory.     

Progesterone metabolism in the gastric mucosa microsomes of guinea pig

The microsomes from guinea pig gastric mucosa were found to convert [4-14C]progesterone to two major metabolites in the presence of NADPH. The gastric metabolizing activity was the highest among the gastrointestinal tissues of guinea pig. 5 alpha-Pregnane-3,20-dione and 3 beta-hydroxy-5 alpha-pregnan-20-one were identified as the major metabolites by thin-layer chromatography and crystallization to constant specific activity, suggesting the presence of steroid 5 alpha-reductase and 3 beta-hydroxysteroid dehydrogenase activities in the gastric mucosa microsomes. Furthermore, time course of progesterone metabolism and analysis of 5 alpha-pregnane-3,20-dione metabolites suggest that the gastric progesterone metabolism is initiated by 5 alpha-reductase and followed by 3 beta-hydroxysteroid dehydrogenase. The progesterone-metabolizing activity was strongly inhibited by SKF 525-A and disulfiram. The activity was also inhibited by methyrapone to a somewhat lesser extent than the above inhibitors. From gastric mucosa microsomes, the progesterone-metabolizing activity was successfully solubilized with 2% digitonin using 0.1 M potassium chloride and 1 mM dithiothreitol, 0.4 mM NADPH and 20% glycerol as stabilizers for the solubilized activity. Among these stabilizers, glycerol was found to be most effective for stabilizing the activity of the solubilized microsomes.     

Percentage binding of testosterone and dihydrotestosterone and unbound testosterone and dihydrotestosterone in rabbit maternal and fetal plasma during sexual organogenesis.

The percentages of bound testosterone (17 beta-hydroxy-4-androsten-3-one; T) and dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one; DHT) and their unbound concentrations were determined in pregnant rabbits and their fetuses from the 18th day of gestation to birth. T and DHT were also measured in fetal testes. In the testis, the total T/total DHT ratio, very high at 22 days (73.7 +/- 15.2), decreased until birth (6.7 +/- 0.8). In male fetuses the concentrations of total and unbound circulating T and DHT were always low and did not show any peak during sexual organogenesis. The percent binding of T (from 73.0 +/- 0.5 to 77.6 +/- 0.6) and DHT (from 76.5 to 83.7 +/- 1.1) in fetuses were similar in both sexes and significantly lower than those measured in mothers (T: from 87.2 +/- 0.6 to 91.6 +/- 0.9; DHT: from 87.3 +/- 0.9 to 93.8 +/- 0.9).     

Skeletal muscle leucine incorporation and testosterone uptake in exercised guinea pigs.

We examined the changes induced by daily treadmill exercise on body weights, plantaris muscle weights, plantaris protein concentrations, and L-leucine-4,5-3H incorporation into plantaris muscles of normal and castrated young male guinea pigs and of castrated animals receiving testosterone replacement therapy, and compared the testosterone-1,2-3H uptake by plantaris muscles of trained normal guinea pigs to that of untrained animals. Trained animals exhibited significantly lower body and muscle weights and greater labeled leucine incorporation into sarcoplasmic and myofibrillar proteins but did not show significant changes in protein concentrations or labeled testosterone uptake. The level of physical activity of the young animals studied appeared to be more important than gonadal endocrine function in altering protein metabolism and muscle and body weights. Because hypertrophy did not occur in the trained plantaris muscles, which had elevated rates of labeled leucine incorporation, it appears that the trained animals had a higher muscle protein turnover rate. It seems unlikely that testosterone plays an important role in these activity-related phenomena.     

Dietary regulation of maternal and fetal cholesterol metabolism in the guinea pig

Studies to determine the effects of pre-natal interventions on maternal and fetal cholesterol homeostasis were carried out in the guinea pig. Guinea pig dams were fed either non-purified guinea pig diet or diet supplemented with either 1.1% of the bile acid binding resin cholestyramine or 0.25% cholesterol. Whole body rates of endogenous cholesterol synthesis were determined by quantitation of [3H]water incorporation into digitonin precipitable sterols in non-pregnant animals and at 40 and 60 days of gestation in the dam and fetus. Maternal hepatic cholesterol synthesis was reduced 87% by dietary cholesterol and was increased 3.5-fold with cholestyramine feeding. Fetal hepatic and peripheral tissue cholesterol synthesis rates peaked at 40 days gestation when peripheral tissue cholesterol synthesis was 5.7-fold higher and hepatic synthesis 6.2-fold greater than the near adult levels observed at 60 days. Cholesterol synthesis in the fetus was relatively insensitive to dietary manipulations; however, maternal cholestyramine treatment did result in a 1.4-fold increase in fetal carcass cholesterol synthesis at 60 days gestation. These data demonstrate that maternal cholesterogenic systems maintain responsiveness to dietary regulation during pregnancy; whereas fetal cholesterol homeostasis is relatively insensitive to dietary cholesterol throughout gestation yet may respond to induction by maternal cholestyramine treatment during the late gestation period.     

Ascorbic acid metabolism and glycolysis in the polymorphonuclear leucocyte of the guinea pig

Exudate leucocytes lost approximately 30% of their original intracellular ascorbic acid content during two hour incubation in glucose medium. The same loss was observed for cells containing initially both high and low levels of ascorbic acid. High concentrations of ascorbic acid in the incubation medium depressed lactic acid production and increased oxygen uptake by the cells. Iodoacetate and fluoride at low concentrations decreased ascorbic acid loss from cells during incubation; at high concentrations they increased loss. Ascorbic acid uptake from the medium was inhibited by iodoacetate but stimulated by fluoride.