ABSTRACT

This study was designed to investigate the differences in testosterone concentrations measured in testicular extracellular interstitial fluid obtained with a push–pull cannula or by post-mortem drip-collection. In the first experiment, testosterone-filled silicone elastomer capsules (2–16 cm lengths) or empty 2 cm capsules were implanted s.c. in adult male rats for 1 week. Animals were then anaesthetized and interstitial fluid was collected with a push–pull cannula for 1 h from one testis in each animal. Testicular and peripheral venous blood were then sampled and supernatant fluid was collected from the dispersed cells of the same testis. The contralateral testis in each animal was removed, and post-mortem interstitial fluid obtained by drip-collection for 20 h at 4 °C. In animals given empty capsules, testosterone concentrations in drip-collected interstitial fluid were significantly (P < 0·01) greater than testicular and peripheral venous blood levels, testicular fluid levels, and levels in interstitial fluid calculated from push–pull cannula samples. The concentrations of testosterone calculated in interstitial fluid collected with a push-pull cannula were never significantly greater than testicular venous blood levels. In animals with testosterone-filled capsules, testosterone concentrations measured in drip-collected interstitial fluid were similar to those calculated from push–pull cannulae samples, and to testicular venous blood levels. In a second experiment, a group of adult male rats was pretreated with aminoglutethimide to block steroidogenesis. Two hours later, interstitial fluid was drip-collected from the testes of these animals and from a group of vehicle-treated controls. For each animal, one testis was placed on ice and interstitial fluid collected for only 10 min, while the contralateral testis was kept at 4 °C and interstitial fluid collected for 20 h. In control animals, testosterone concentrations in interstitial fluid collected for 20 h were significantly (P < 0·01) greater than those in interstitial fluid collected for 10 min. In animals pretreated with aminoglutethimide, testosterone concentrations at 10 min and 20 h were not significantly different, and did not differ from those in control samples collected for 10 min.

We believe these results support earlier suggestions that the post-mortem drip-collection technique may give misleading results, and indicate that testosterone synthesis and secretion continues after isolation of the testis. This may also be the case with other Leydig cell products.

Journal of Endocrinology (1989) 121, 303–309

ABSTRACT

We have used a push–pull cannula to collect interstitial fluid from the testes of anaesthetized rats at various times after a single injection of human chorionic gonadotrophin (hCG; 50 IU), and compared the levels of testosterone in this fluid with the levels in testicular and peripheral venous blood collected at the same times. Following hCG injection, significant increases in testosterone concentrations were observed in all fluids with notable peaks occurring in interstitial fluid at 2, 8 and 24 h, in testicular venous blood at 2, 8 and 30 h, and in peripheral venous blood at 2, 8, 24 and 72 h. The results demonstrate for the first time that changes in testosterone concentrations in interstitial fluid can be different from those in testicular venous blood. In addition, when testosterone levels in interstitial fluid were compared with levels in testicular venous blood at each time-point, the results suggested that the partitioning of testosterone between these two compartments can be regulated. Furthermore, the changes in both interstitial fluid and testicular venous blood levels of testosterone do not always parallel those in peripheral venous blood, suggesting that changes in testicular blood flow and peripheral clearance rates of testosterone may also be important in the control of circulating testosterone concentrations.

Journal of Endocrinology (1989) 121, 311–316

To test the interaction of androgen and inhibin feedback on the pituitary gland, inhibin-type feedback from the testes was reduced when they were made aspermatogenetic by bilateral ligation of the efferent ducts or local heating (43 °C for 30 min). There were only minor effects on the subsequent response of the pituitary gland to the removal of androgen feedback by the administration of antiserum against testosterone or by castration. However, in the antiserum-injected animals the steroidogenic response of the testis to the increased serum concentrations of LH was less in aspermatogenic than in control rats. Furthermore, unilateral aspermatogenesis was associated with reduced testosterone output by the treated testis and with compensatory increased output by the contralateral control testis, despite the absence of significant changes in serum LH and normal peripheral levels of testosterone. This suggests that the tubules can regulate the responsiveness of the Leydig cells to LH.

It has already been reported that rete testis fluid (RTF) from rams and boars contains something which reduces the uterine response to human chorionic gonadotrophin in rats and mice, presumably by reducing the secretion of endogenous gonadotrophin by the recipient animals (Setchell & Sirinathsinghji, 1972). These observations have now been extended by measurements of the concentrations of follicle-stimulating (FSH) and luteinizing hormones (LH) in the plasma of rats injected with RTF. Three groups of recipient rats were used: 21-day-old females, adult, intact males, weighing between 250 and 400 g, and adult males of similar age, castrated 3 weeks previously. Ram RTF was collected at 4 °C, and the spermatozoa were removed by centrifugation (3000 g for 15 min); the fluid was kept at −20°C until used. The fluid was injected intraperitoneally, twice daily, 0·5 ml at 09.00 h and 1·0 ml at 17.00 h; some of the fluid was concentrated

The subcutaneous injection of human chorionic gonadotrophin (HCG) into adult male rats caused appreciable rises in capillary permeability and lymph flow in the testis, accompanied by smaller rises in the volume of extratubular, extracellular fluid. Most of these changes were already apparent 8 h after injection, but became progressively greater during the next 12 h. Testicular blood flow was unchanged at 12 h but increased slightly between 12 and 16 h after injection. The primary effect is probably the increase in capillary permeability. The timing of these changes suggests that HCG does not affect the capillaries directly, but it would seem that the changes are due to some substances secreted by the testis in response to the HCG. It is clear that these changes will have important influences both on the access to the testicular cells of peptide hormones in the blood and also on the passage into the venous blood of hormones secreted by the testis.

ABSTRACT

The capacity of the anterior pituitary gland and testes in mature bulls (705±9 (s.e.m.) kg body wt, n = 4) to respond to graded doses of LH-releasing hormone (LHRH) was assessed relative to endogenous profiles of LH and testosterone secretion. Endogenous hormone profiles were determined by bleeding bulls at 20-min intervals for 12 h. Responses to LHRH were assessed on successive days after single intravenous injections of 1, 5, 10, 50 or 100 ng LHRH/kg body wt. Blood samples were taken at −40, −20, 0, 10, 20, 30, 40, 60 and 120 min relative to LHRH injection. During a 12-h bleed bulls showed spontaneous pulses of LH and testosterone which had peak amplitudes of 2·6±0·5 μg/l and 44·5 ± 7·1 nmol/l respectively. Respective peak LH (μg/l) and testosterone (nmol/l) responses to LVRH were as follows: 1 ng LHRH (3·0±0·7: 47·3±4·1); 5 ng LHRH (8·0±1·2; 52·8 ± 6·2); 10 ng LHRH (11·1±2·3; 57·7 ± 9·1); 50 ng LHRH (19·2±2·8; 47·9±8·6); 100 ng LHRH (19·1±4·7; 43·9 ±6·4). A dose of 1 ng LHRH/kg produced LH and testosterone responses which were comparable in amplitude to spontaneous peaks in the respective hormone. There was a linear (y = 0·28x+5·72; r = 0·81) increase in the LH response to doses of LVRH between 1 and 50 ng/kg; corresponding testosterone responses showed no relationship with the dose of LHRH. The capacity of the anterior pituitary gland to release amounts of LH eight to ten times in excess of those secreted during spontaneous peaks suggests that (1) there exists a large releasable store of LH in the anterior pituitary gland and (2) hypothalamic LHRH is a limiting factor in gonadotrophin secretion. In contrast to LH release, the androgenic response of the testes to acute gonadotrophic stimulation is determined largely by prevailing steroidogenic activity.

J. Endocr. (1984) 103, 371–376

SUMMARY

The effect of s.c. injections of cadmium chloride (3 μmole/100 g. body wt.) on the blood flow and vascular permeability of the testis, epididymis and accessory reproductive organs of rats has been examined. Sapirstein's indicator fractionation technique was used to measure blood flow with [¹³¹I]iodoantipyrine and [⁸⁶Rb]-rubidium chloride. A rubidium-rejecting compartment was found in the testis similar to, but smaller than, that in the brain and pineal body.

Testicular blood flow started to decrease within 3 hr. of giving cadmium (Cd) and by 12 hr. was only 2–9 % of the control values; it then started to recover but after 14 days it was still only 31 % of the control values.

Apart from a small reduction of blood flow to the first part of the head of the epididymis 6 hr. after Cd administration, blood flow was not strikingly reduced in any part of the epididymis by Cd treatment. However, blood flow to all parts of the epididymis had increased markedly when examined 7 days after giving Cd; this was most evident in the first part of the head of the epididymis.

Blood flow through the accessory reproductive organs was reduced within 6 hr. of Cd injection. Blood flow in the seminal vesicles returned to normal between 1 and 14 days after treatment but blood flow in the prostate gland did not recover.

The movement of albumin from intravascular to extravascular compartments was used as an index of vascular permeability. This index increased in the testis in the period 1–6 hr. after Cd administration and the change occasionally occurred before blood flow decreased. A similar increase was seen in the first part of the head of the epididymis 3–6 hr. after Cd, but no change was seen in the rest of the epididymis.

The evidence suggests that Cd acts by damaging the endothelium of the capillaries in the testis leading to prolonged stoppage of blood flow which would lead to hypoxia in the spermiogenic epithelium.

SUMMARY

The entry of ¹²⁵I-labelled ovine follicle-stimulating hormone (FSH) and human serum albumin into the seminiferous tubules of rams has been studied by measuring radioactivity in blood plasma and rete testis fluid after an intravenous injection of the labelled protein. After the injection of FSH, radioactivity/mg total protein in rete testis fluid exceeded that in blood plasma from the first day onwards, but after the injection of human serum albumin, radioactivity/mg total protein in rete testis fluid only reached that in plasma after 4–5 days and never exceeded it. Protein-bound radioactivity disappeared from the blood more quickly after an injection of FSH than after an injection of albumin.

The volume of distribution for ovine FSH in the testes of rats was greater than that for human serum albumin. The volume of distribution for FSH was greater, in absolute terms, in the testes with the efferent ducts ligated 24 h previously than in the contralateral control testes when the FSH was injected at the time of efferent duct ligation. The volume of distribution for albumin was slightly less in the ligated testes than in the control testes. This suggests that FSH but not albumin had penetrated into the fluid trapped inside the testis. The liver and kidney had much higher concentrations of protein-bound radioactivity per unit weight than did the testis after the injection of FSH, so it does not seem that FSH is selectively taken up by the testis.

SUMMARY

Blood flow, capillary permeability and the entry of rubidium into the testis, epididymis, skeletal muscle and brain of male rats were examined within 6 hr. of giving an s.c. injection of cadmium chloride (3 μmole/100g. body wt). Sapirstein's (1958) indicator fractionation technique was used to measure blood flow with [¹²⁵I]iodoantipyrine and simultaneously capillary permeability and rubidium uptake were assessed using ¹³¹I-labelled human serum albumin and [⁸⁶Rb]rubidium chloride respectively.

Blood flow in the testis and the initial segment of the caput of the epididymis increased in the first 2 hr. after cadmium administration, returned to control levels at 3 hr., and thereafter sharply decreased. Labelled albumin began to accumulate in extravascular compartments 3–4 hr. after cadmium; in the head of the epididymis this increase in capillary permeability appeared earlier than in the testis and preceded the fall of blood flow.

The limited transport of rubidium into the seminiferous tubules was again observed and used as a criterion of tubular integrity. The uptake of ⁸⁶Rb by the testis increased within 2 hr. of giving cadmium and thus preceded the extravascular transport of albumin from the capillaries. This is the earliest indication of cadmium damage to the tubules so far reported. There were no systematic changes in these parameters in the rest of the epididymis, skeletal muscle or brain.

ABSTRACT

This study aimed to obtain a better understanding of the relationship between circulating thyroxine (T₄) concentrations and reproductive endocrine function in the ram. Mature Merino rams were thyroidectomized and supplemented with 0, 30, 100 and 300% of normal T₄ for 10 weeks. Thyroidectomy had no apparent effect on spermatogenic function but interfered with sperm maturation, the latter being returned to normal by 30% T₄ replacement. Circulating testosterone levels were reduced by thyroidectomy and restored to control levels by 30% T₄; when T₄ levels were supranormal (300%), circulating testosterone levels were again reduced. The lowered circulating testosterone levels in thyroidectomized rams occurred as a result of suppressed testosterone secretion from the testis, observed under basal conditions and also following LH-releasing hormone (LHRH) and human chorionic gonadotrophin injection. In thyroidectomized rams, sex hormone binding globulin (SHBG) levels were depressed without changes in testosterone clearance rate (TCR), while in rams with supranormal T₄ levels, TCR was increased without changes in SHBG levels. Subnormal levels of T₄ also restored to normal the reduced LH pulse frequency in thyroidectomized rams. Reduced LH pulse frequency, together with diminished LH release following LHRH injection in thyroidectomized rams, suggested effects of T₄ at the hypothalamo-pituitary axis. The present study demonstrates that complete lack of thyroid hormones suppresses normal reproductive endocrine function in the ram, but that this can be restored to normal by 30% T₄ replacement. The results support the theory that T₄ plays a permissive rather than a regulatory role in reproductive function in males.

J. Endocr. (1986) 111, 245–253