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Biomedical subjects

A R Bourne

Publications and source records attributed to A R Bourne.

At least 19 recordsLinked to original sources
PubMed1989

The in vitro biosynthesis of epitestosterone and testosterone from C19 steroid precursors in the testis of the lizard Tiliqua rugosa.

The metabolism of androgens in the testis of the lizard Tiliqua rugosa has been studied in vitro by incubating cellular homogenates with radiolabeled C19-steroid substrates. The identification 17 beta-oxidoreductase and 3 beta-hydroxysteroid dehydrogenase/isomerase activities. Aromatase, 5 alpha-reductase, and 17 alpha/beta-epimerase activities were not detected. The 17 alpha-oxidoreductase activity was temperature dependent (maximal at 32 degrees), while the 17 beta-oxidoreductase activity was temperature independent. Time yield and dual-label studies indicated that testosterone biosynthesis mainly involves the 4-ene pathway (via androstenedione), whereas the formation of epitestosterone uses both the 4-ene and 5-ene (via 5-androstene-3 beta, 17 alpha-diol) pathways. The function of alternative pathways in androgen biosynthesis is discussed, as is the role of temperature in the intratesticular regulation of androgen production.

Androstenediol↗
PubMed1987

Identification of testosterone sulfate in the plasma of the male lizard Tiliqua rugosa.

Plasma (solvolyzed and unsolvolyzed) from the male lizard Tiliqua rugosa was analyzed using gas chromatography, high-performance liquid chromatography (HPLC), and mass spectroscopy. HPLC with electrochemical detection was also used to characterize ketosteroid conjugates. Testosterone was identified in the solvolyzed plasma extract, and a compound corresponding to testosterone sulfate was detected in unsolvolyzed extracts. Concentrations were approximately 500 nmol/liter in intact male plasma, less than 100 nmol/liter in castrates, and undetectable in female plasma. Steroid glucuronides appeared to be absent from plasma. Epitestosterone conjugates were not detected, although the free steroid is found in high concentrations in T. rugosa. The presence of testosterone sulfate in the blood of T. rugosa may indicate a possible role for sulfoconjugates in controlling the availability of biologically active androgens.

Animals↗
PubMed1986

Annual cycles of plasma and testicular androgens in the lizard Tiliqua (Trachydosaurus) rugosa.

Androgen production during the annual reproductive cycle was investigated in the male scincid lizard Tiliqua (Trachydosaurus) rugosa. Concentrations of testosterone and epitestosterone were measured in plasma and testis (incubated and nonincubated) using radioimmunoassay. Morphological and histological techniques were used to determine the anatomical changes in the testis. Mating behavior was observed during spring, and sperm were most numerous in the testis at this time. Histological evidence and changes in testicular weight indicated that spermatogenesis begins in autumn and culminates in spring. Testicular regression occurred soon after mating. Plasma concentrations of both androgens were maximal during spring and minimal during summer. The maximal concentrations were approximately 500 and 150 nmol/liter (epitestosterone and testosterone, respectively). The minimal plasma concentrations were 250 and 15 nmol/liter, respectively. Plasma and testicular androgen cycles followed a pattern similar to that of the spermatogenetic cycle, suggesting the possible involvement of one or both of these androgens in the control of spermatogenesis and mating behavior in these lizards.

Androgens↗
PubMed1986

Changes in blood progesterone concentration during pregnancy in the lizard Tiliqua (Trachydosaurus) rugosa.

Progesterone concentrations during pregnancy were measured in the plasma of the viviparous lizard (scincid) Tiliqua (Trachydosaurus) rugosa, using a radioimmunoassay specific for progesterone. The length of gestation in this Australian lizard was 140-170 days. The average number of young was 2.8 and the mean neonatal weight 58 g (maternal body weight 500-700 g). The mean concentration of progesterone was greatest (7.2 nmol/l) during the second trimester of pregnancy; mean values during the first and third trimesters, and in non-pregnant females, were 1.8, 0.9 and 0.2 nmol/l respectively.

Animals↗
PubMed1986

Effect of temperature on the seasonal production of testicular androgens, in vitro, by the lizard Tiliqua rugosa.

The effect of temperature on the seasonal production of testicular androgens, in vitro, was examined in the scincid lizard Tiliqua (Trachydosaurus) rugosa. Testicular tissue was incubated, in vitro, at various temperatures (18, 25, 32 and 37 degrees C). Endogenous androgens, testosterone and epitestosterone, were measured by radioimmunoassay. Epitestosterone production was maximal at 37 degrees C and minimal at 18 degrees C. There was no consistent effect of incubation temperature on testosterone production. Incubation temperature had no effect on the seasonal pattern of androgen production. The results suggest that temperature may play a part in the regulation of androgen biosynthesis in T. rugosa.

Acclimatization↗
PubMed1985

Identification of epitestosterone in the plasma and testis of the lizard Tiliqua (Trachydosaurus) rugosa.

Blood and testicular extracts of the scincid lizard Tiliqua (Trachydosaurus) rugosa were analyzed using thin-layer, column, and high-performance liquid chromatography. The major androgens isolated were epitestosterone, testosterone, and androstenedione. Epitestosterone was characterized by chromatography in several systems, and by derivative formation. Epitestosterone was further identified in testicular extracts by gas chromatographymass spectrometry. Immunoreactive material was detected in tissue extracts using an antiserum specific to epitestosterone. The maximum concentration of epitestosterone in blood, measured by radioimmunoassay, was four times that of testosterone (approximately 900 and 200 nmol/l, respectively). Epitestosterone could not be detected in the blood of intact females and the concentration of this steroid was low in castrate males. The maximum testicular concentrations (pmol/testis) were 390 (nonincubated) and 2050 (incubated) for epitestosterone, and 2025 (nonincubated) and 1040 (incubated) for testosterone. Both plasma and testicular concentrations showed considerable seasonal variation. The identification of endogenous epitestosterone confirms the results of earlier investigations using radioactive substrates. The occurrence of this steroid as a major product of the testis in T. rugosa is discussed in relation to androgens in reptiles and other vertebrates.

17-alpha-Hydroxyprogesterone↗
PubMed1985

Steroid biosynthesis in turtle testes.

Testicular metabolism of radiolabelled substrates (pregnenolone, progesterone and androstenedione) was examined in two species of turtles, Pseudemys scripta and Sternotherus odoratus. Chemical methods (chromatography, derivative formation and crystallization) identified testosterone (in both species) and 5 alpha-androstane-3 beta,17 beta-diol (in S. odoratus) as products. Tentative identifications were also made of 20 beta-hydroxypregn-4-en-3-one in both turtles. Chromatographic profiles indicated the presence of several other C19- and C21-steroids. In S. odoratus, changes in proportions of the two major C19-compounds (testosterone and the 5 alpha-androstanediol) suggest a "switch" in the enzymatic pathways which resembles that associated with maturation in the rat. This enzymatic switch may be associated with the annual testicular cycle of the adult turtle.

Androstenedione↗
PubMed1982

Plasma insulin response and food intake in pseudopregnant rats.

1. Plasma insulin response to an intravenous glucose injection was measured in anaesthetised pseudopregnant and non-pregnant rats. Food intakes and body composition were also compared in pseudopregnant and non-pregnant animals. 2. The insulin responses and food intakes were greater in the pseudopregnant group. 3. Pseudopregnancy increased the fat-free dry weight of the animals and there was a tendency for the proportion of fat to be increased. 4. The results provide further evidence to indicate that in the rat progesterone plays a significant part in increasing insulin secretion during pregnancy.

Animals↗
PubMed1979

Synthesis of steroids by echidna (Tachyglossus aculeatus) testis and the effects of gonadotrophin administration.

After administration of hCG and PMSG to male echidnas (in non-breeding state) the testis to body weight ratio increased 3-fold and the diameter of the seminiferous tubules doubled, but spermatogenesis was not induced. The major conversion product of testicular homogenate with [4-14C]progesterone as substrate was 17 alpha-hydroxyprogesterone (4% in untreated and 29% in treated echidnas). Testosterone (5%), androstenedione (16%) and 17 alpha,20 beta-dihydroxypregn-4-en-3-one (7%) were also obtained in gonadotrophin-treated animals. In untreated animals these steroids were present in minor amounts (less than 1%).

Androstenedione↗
PubMed1978

Seasonal variation in steroid biosynthesis by the testis of the lizard Tiliqua Rugosa.

1. Seasonal change in the biosynthesis of androgens by testicular tissue from a scincid lizard Tiliqua rugosa has been studied in vitro using [7-3H]pregnenolone and [4-14C]progesterone as substrates. 2. Evidence is presented for the synthesis of epitestosterone, testosterone, androstenedione, 17 alpha-hydroxyprogesterone, 20 beta-hydroxypregn-4-en-3-one, and 17 alpha, 20 beta-dihydroxypregn-4-en-3-one. 3. Epitestosterone was the major conversion product. Its yield was highest (68%) during summer and lowest (14%) during spring. The yield of testosterone was maximal (10%) during spring (mating season). The production of 20 beta-hydroxypregn-4-en-3-one was highest during spring and undetectable during summer. 4. Histological evidence and changes in testicular weight indicated that spermatogenic activity was greatest during spring. Pronounced regression of the testis occurred immediately after the breeding season and lasted until autumn.

Acclimatization↗
PubMed1975

Some effects of different dietary carbohydrates on pregnancy and lactation in rats.

Female rats were fed from weaning on diets with sucrose, starch, glucose or fructose as the carbohydrate source. Animals were killed at various stages throughout pregnancy and early lactation. Maternal plasma triglycerides (TG), cholesterol, free fatty acids, glucose, insulin and corticosteroids were measured. Lipogenic activity was assayed in the livers, adipose tissue and mammary tissue, and the results compared with those from non-pregnant rats. Insulin, corticosteroids and hepatic lipogenesis were also assayed in the embryos and in newborn pups. Dietary sucrose and fructose produced a significantly higher concentration of plasma TG in the non-pregnant, pregnant and lactating rats than did starch and glucose. All the diets led to an increase in TG concentration at the 20th day of pregnancy, which returned to the original concentration 2 days post-partum. The hypertriglyceridaemia of late pregnancy was accentuated by the feeding of sucrose and fructose. Maternal concentrations of plasma glucose were significantly reduced towards the end of pregnancy in all dietary groups. The replacement of starch by sucrose, or of glucose by fructose, enhanced hepatic lipogenesis. Fructose but not sucrose depressed fat synthesis in the adipose tissue. Hepatic fatty acid synthetase activity was increased in late pregnancy on all diets except that with starch. Late pregnancy intensified hepatic lipogenesis in rats fed sucrose or fructose. The results are discussed in relation to the metabolic changes during pregnancy and to sucrose feeding.

Adipose Tissue↗