The importance of glucose for the freezing tolerence/intolerence of the anuran amphibians Rana catesbeiana and Bufo paracnemis

Several species of terrestrially hibernating frogs, turtles and inserts have developed mechanisms, such as increased plasma glucose, anti-freeze proteins and antioxidant enzymes that resist to freezing, for survival at subzero temperatures. In the present study, we assessed the importance of glucose to cryoresistance of two anuran amphibians: the frog Rana catesbeiana and the toad Bufo paracnemis. Both animals were exposed to -2 degrees Celsius for measurements of plasma glucose levels, liver and muscle glycogen content, haematocrit and red blood cell volume. Frogs survived cold exposure but toads did not. Blood glucose concentration increased from 40.35 + 7.25 to 131.87 + 20.72 mg/dl (P < 0.01) when the frogs were transferred from 20 to -2 degrees Celsius. Glucose accumulation in response to cold exposition in the frogs was accompanied by a decrease (P < 0.05) in liver glycogen content from 3.94 + 0.42 to 1.33 + 0.36 mg/100 mg tissue, indicating that liver carbohydrate reserves were probably the primary carbon source of glucose synthesis whereas muscle carbohydrate seems unimportant. In the toads, the cold-induced hyperglycaemia was less (P < 0.05) pronounced (from 27.25 + 1.14 to 73.72 + 13.50 mg/dl) and no significant change could be measured in liver or muscle glycogen. Cold exposition had no effect on the haematocrit of the frogs but significantly reduced (P < 0.01) the haematocrit of toads from 20.0 + 2.1 per cent to 5.8 + 1.7 per cent due to a decreased red blood cell volume (from 1532 + 63 70 728 + 87 mm3). When toads were injected with glucose, blood glucose increased to levels similar to those of frogs and haematocrit did not change, but this failed to make them cryoresistent. In conclusion, the lack of cold-induced glucose catabolism may not be the only mechanism responsible for the freeze intolerance of Bufo paracnemis, a freeze-intolerant species.

Decreased spermatogenic and androgenic testicular functions in adult rats submitted to immobilization-induced stress from prepuberty

We investigated whether chronic stress applied from prepuberty to full sexual maturity interferes with spermatogenic and androgenic testicular functions. Male Wistar rats (40 days old) were immobilized 6 h a day for 60 days. Following immobilization, plasma concentrations of corticosterone and prolactin increased 135 per cent and 48 per cent, respectively, while plasma luteinizing hormone and testosterone presented a significant decrease of 29 per cent and 37 per cent, respectively. Plasma concentration of follicle-stimulating hormone was not altered in stressed rats. Chronic stress reduced the amount of mature spermatids in the testis by 16 per cent and the spermatozoon concentration in the cauda epididymidis by 32 per cent. A 17 per cent reduction in weight and a 42 per cent decrease in DNA content were observed in the seminal vesicle of immobilized rats but not in its fructose content. The growth and secretory activity of the ventral prostate were not altered by chronic stress.

Sexual development of male Wistar rats

1. Sexual development was investigated in male Wistar rats from 22 to 97 days of age by morphometric, biochemical and radioimmunological methods. 2. The first significant increase of plasma testosterone (T) occurred from 40 to 50 days of age and a progressive enhancement was observed thereafter to a maximum at 76 days (5.4 +/- 0.9 ng/ml). From that time onward, plasma T was gradually depressed to adult levels at 97 days of age (2.0 +/- 0.3 ng/ml). Plasma prolactin increased in parallel to T, reaching a maximum at 76 days (9.2 +/- 0.9 ng/ml) and attaining a lower plateau by 83 to 97 days of age (5.0 +/- 0.5 ng/ml). A small but significant increase was observed in plasma luteinizing hormone from 22 to 83 days of age. Plasma follicle stimulating hormone was high at 22 days, increased to a maximum at 40 days (15.4 +/- 0.6 ng/ml) and fell slowly to a lower plateau by 76 to 97 days of age. 3. Fructose content in the ventral prostate increased abruptly from 50 to 63 days of age (148.8 +/- 19.8 micrograms) and no significant change was observed thereafter. A progressive increase in the seminal vesicle fructose content was observed from 40 to 63 days (45.6 +/- 2.8 micrograms) when a plateau was reached. 4. The evolution of the germinal epithelium was investigated in cross-sections of seminiferous tubules analyzed at random for the presence of the most advanced germ cell and also for sperm production (estimated by the number of spermatids in stages 15 to 18 of spermiogenesis).(ABSTRACT TRUNCATED AT 250 WORDS)

Prepubertal development of rat prostate and seminal vesicle following chemical sympathectomy with guanethidine

1. The internal genital organs of prepubertal, 21-day old male Wistar rats were sympathectomized by ip injection of guanethidine (G), at doses of 5 mg/kg per day (N = 10) or 10 mg/kg per day (N = 10), for 20 days. Controls (N = 10) received saline. 2. Plasma testosterone level (measured by radioimmunoassay) decreased significantly in sympathectomized rats from 4.11 +/- 0.57 to 1.76 +/- 0.37 ng/ml (5 mg/kg G) and to 1.17 +/- 0.26 ng/ml (10 mg/kg G). Plasma levels of luteinizing and follicle-stimulating hormones and of prolactin were unaltered. 3. Chemical denervation caused a significant decrease in ventral prostate wet weight from 74.3 +/- 5.5 to 59.3 +/- 4.7 mg (5 mg/kg G) and to 54.6 +/- 4.1 mg (10 mg/kg G) and in seminal vesicle wet weight from 36.5 +/- 6.8 to 31.7 +/- 5.2 mg (5 mg/kg G) and to 21.3 +/- 1.6 mg (10 mg/kg G). 4. The potential secretory activity of the prostate (measured in terms of fructose content) decreased significantly in guanethidine-treated rats from 0.38 +/- 0.02 to 0.30 +/- 0.02 mg/g (5 mg/kg G) and to 0.20 +/- 0.02 mg/g (10 mg/kg G). The seminal vesicle fructose content (0.33 +/- 0.04 mg/g for controls), however, was not altered by chemical denervation. 5. Our data suggested that sympathetic neurons may be involved in the control of LH receptors, at least in the prepubertal phase of sexual development. They may also be directly related to growth and secretory activity of the male accessory sex glands

Effect of low-intensity pulsed ultrasound on prepubertal rat testis

The testes of prepubertal male rats (N -12) aged 21 days were stimulated with low-intensity pulsed ultrasound (1.5-MHz frequency, 1-KHz repetion pulse rate, 200-*s pulse width, 30-V peak-to-peak amplitude and 20-mW/cm* intensity) applied to the skin for 20 min/day for 7 days. Control rats (N-8) were manipulated in the same manner but not submitted to ultrasound. Ultrasound stimulation promoted a significant increase in plasma testosterone (62%) leading to a significant increase in seminal vesicle relative weight (35%) as well as an increase in the fructose (92%) and DNA (200%) contents of the gland. No differences were detected between ultrasound-treated and control animals, in terms of body weight and the relative weights of testis, cauda epididymidis, testis DNA and mitosis

Análise morfométrica do testículo e epididimo do rato na fase inicial da intoxicaçäo pelo chumbo

Ratos machos adultos foram intoxicados por ingestäo "ad libitum" de acetato de chumbo nas concentraçöes de 0,5 g/1 e 1,0 g/l, durante 90 dias. Ao final do período experimental, a intoxicaçäo foi confirmada pelo aumento acentuado na concentraçäo de chumbo no sangue, aliado `a diminuiçäo dos valores de hematócrito e hemoglobina e aumento da glicemia. Nesta fase inicial da intoxicaçäo, näo se observaram alteraçöes no diâmetro dos túbulos seminíferos, na altura do epitélio germinativo, no ritmo do processo espermatogênico e na produçäo de espermatozóides. A cabeça do epidídimo näo apresentou também qualquer alteraçäo estrutural. A cauda do epidídimo, por outro lado, exibiu aumento significativo no diâmetro do ducto e diminuiçäo na altura do epitélio. A concentraçäo de espermatozóides armazenados na regiäo caudal do epidídimo mostrou-se significativamente aumentada nos aniamis tratados com chumbo. Os resultados revelam o envolvimento precoce da cauda do epidídimo na intoxicaçäo pelo chumbo, e sugerem um distúrbio no mecanismo neuroendócrino que controla as múltiplas funçöes epididimárias