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Biomedical subjects

S S Howards

Publications and source records attributed to S S Howards.

At least 91 records · Page 5Linked to original sources
PubMed1981

Osmotic effects of intravenous contrast agents on renal function.

Because of renewed interest in renal insufficiency after excretory urography a set of experiments was designed to determine the effects of high dose intravenous contrast agents on renal blood flow and glomerular filtration rate. A reproducible decrease in renal blood flow and glomerular filtration rate was noted with high dose intravenous contrast agents and an osmotically similar solution without the radiographically active compound. The results are discussed in light of clinical significance.

Animals↗
PubMed1981

Influence of surgically induced varicocele on testicular blood flow, temperature, and histology in adult rats and dogs.

Varicocele had been repeatedly implicated as a cause of infertility in selected men, although neither a causal relationship nor a mechanism has been documented. The purpose of this investigation was to create a varicocele model in animals and to study the subsequent alterations in testicular physiology. Secondary dilatation of the left internal spermatic vein was achieved either by partial ligation of the left renal vein in rats and dogs or by surgical destruction of the valve of the left testicular vein in a second group of dogs. 1 mo after partial ligation in the rats and 3 mo after partial ligation or valve destruction in the dogs, testicular blood flow was measured using Strontium 85 (SR-85)-labeled microspheres (15 +/- 1.1 micrometer). Intratesticular temperature was measured with a Bailey needle probe thermometer and biopsies were obtained for histologic sections. Mean testicular blood flow in milliliters per minute per 100 g was significantly greater in the partially ligated rats; right testis control 26 +/- 2, left testis control 24 +/- 2 compared to right testis experimental 35 +/- 3, left testis experimental 35 +/- 4 (p less than 0.02). Dogs undergoing either partial vein ligation or valve destruction showed similar increases in mean testicular blood flow; right testis control 8 +/- 1, left testis control 8 +/- 1 vs. right testis experimental 16 +/- 3, left testis experimental 18 +/- 4 (p less than 0.01). The mean difference between intratesticular and intraperitoneal temperature in control rats was significantly higher (4.02 +/- 0.25 degrees C right testis, 3.77 +/- 0.14 degrees C left testis), than rats who underwent partial vein ligation (right testis 2.14 +/- 0.09 degrees C, left testis 2.34 +/- 0.12 degrees C) (p less than 0.001). Control dogs also had a significantly higher mean difference between intratesticular and rectal temperatures; (right testis control 3.61 +/- 0.42 degrees C, left testis control 3.60 +/- 0.40 degrees C) than the partially ligated or valve destruction dogs (right testis 2.31 +/- 0.17 degrees C, left testis 2.67 +/- 0.32 degrees C) (p less than 0.05). In addition, histologic evaluation revealed abnormalities in spermatogenesis in some of the animals. Thus, venous dilatation secondary to partial vein ligation or testicular vein valve obliteration is followed by large bilateral increases in testicular blood flow in these two species. A consequence of this increased flow is an elevation in bilateral testicular temperature, which it is postulated, leads to impaired spermatogenesis in some of the animals. In selected men varicocele may impair spermatogenesis by a similar physiologic mechanism.

Animals↗
PubMed1981

Permeability characteristics of the epithelium in the rat caput epididymidis.

Micropuncture techniques were used to study the in-vivo transfer of radioactive compounds of different molecular weights across the epithelium of the rat caput epididymidis. Small molecular weight compounds such as 3H2O and [14C]urea equilibrated in less than 20 min and 2 h respectively after intravenous injection. Compounds of larger molecular weight ([3H]polyethylene glycol, [3H]inulin and 125I-labelled bovine serum albumin) entered the lumen more slowly and reached less than 5% of blood plasma concentrations 3 h after injection. The luminal concentration of [3H]inulin remained below 7% of the blood level for 18 h. These results demonstrate that a permeability barrier exists in the epithelium of the rat caput epididymidis.

Animals↗
PubMed1981

Effect of oestradiol valerate on the rat blood--testis and blood--epididymal barriers to [3H]inulin.

Micropuncture samples were taken from rats treated with 2.9 mg oestradiol valerate/day for 14 days, sham injected or untreated. Oestradiol valerate treatment reduced testicular weight and serum testosterone concentrations (P less than 0.05), but did not alter the movement of [3H]inulin into seminiferous tubules or those of the cauda epididymidis. [3H]Inulin concentrations in the seminiferous tubule fluids were always less than 8% of blood isotope concentrations, and those in cauda epididymal tubuule fluid were always less than 5% of blood isotope concentrations. It was concluded that the maintenance of the anatomical component of the blood--testis and blood--epididymal barriers (cell--cell tight junctions) is not androgen-dependent.

Animals↗
PubMed1981

Cyclophosphamide, vincristine, and the blood testis barrier.

The blood testis barrier has been implicated in the pathogenesis of testicular relapse of childhood acute leukemia by forming a "sanctuary site" for leukemic cells. Experiments were conducted to test the transport of carbon 14 cyclophosphamide and tritiated vincristine across the blood testis barrier. Both cyclophosphamide and vincristine crossed the blood testis barrier. However, other factors such as the transport of immunoglobins and leukocytes across the blood testis barrier may interact in the pathogenesis of leukemic testicular relapse.

Animals↗
PubMed1981

The blood epididymal barrier to [3H]-inulin in intact and vasectomized hamsters.

The net transport of [3H]-inulin into the fluids of the hamster seminiferous and caput, corpus, and cauda epididymal tubules was examined in both intact animals and those vasectomized 10 months previously. Mean isotope concentrations in reproductive tract tubule fluids did not exceeded 10 per cent of blood plasma isotope concentrations during the experiment. There were no significant differences in net transport of [3H]-inulin into any of the tubule fluids sampled. Ten months after vasectomy, the seminiferous tubule, and all regions of the epididymal tubule retain the capacity to exclude [3H]-insulin. Thus in the hamster 10 months after vasectomy, the blood testis and blood epididymal barriers to inulin are intact.

Animals↗
PubMed1980

Daily spermatozoal production and epididymal spermatozoal reserves of the human male.

Testicular and epididymal spermatozoal reserves were determined for 11 healthy men, a vasectomized man and 12 other men. For healthy men testis weight (19 testes) averaged 16.9 plus or minus 1.2 gm. and daily spermatozoal production was 4.25 times 10(6) per gm. (range equals 1.4 to 6.3 times 10(6) per gm.). Based on our total sample (23 patients) 67 per cent of the men 20 to 50 years old probably produce between 45 times 10(6) and 207 times 10(6) spermatozoa per day. Daily spermatozoal production was normal in 1 vasectomized man. Epididymal reserves of healthy men totaled 182 times 10(6) spermatozoa per epididymis, of which 26 per cent were in the caput, 23 per cent in the corpus and 52 per cent in the cauda. The interval between any previous ejaculation and death was unknown but we assumed that these values are typical for men copulating or masturbating every 1 to 7 days. Extragonadal spermatozoal reserves totaled approximately 440 times 10(6), of which less than 225 times 10(6) would be available for ejaculation in the ductuli deferentia and caudae epididymides. Transit time of spermatozoa through the caput, corpus and cauda epididymidis was estimated as 0.72, 0.71 and 1.76 days. In a vasectomized man extragonadal reserves totaled 7 times 10(9) spermatozoa or about 75 days of production by the testes. Thus, spermatozoal production in man is much less efficient than in other mammals, the extragonadal reserves of spermatozoa are small and maturation of spermatozoa in the caput plus corpus epididymidis occurs in less than 2 days. In terms of these quantitative characteristics the reproductive capacity of man is considerably less than that of a rhesus monkey.

Animals↗
PubMed1980

Serum prolactin in organic and psychogenic impotence.

Elevated levels of serum prolactin in patients with pituitary tumors have been associated with hypogonadism, frequently manifested in men as impotence and/or loss of libido. The purpose of our study was to test the hypothesis that psychogenic and/or organic impotence may be a manifestation of a relative hyperprolactinemic state. We studied 30 men with the known diagnosis of impotence: 17 organic and 13 psychogenic. There were 11 normal, sexually active men used as controls. Serum prolactins were determined with the radioimmunoassay technique. There was no significant differences in serum prolactin levels among control, organic impotent and psychogenic impotent groups. Impotence does not seem to be related to hyperprolactinemia in men in the absence of pituitary disease.

Adult↗
PubMed1980

Rapid regression of pituitary prolactinomas during bromocriptine treatment.

Therapy for large prolactinomas remains controversial. Surgery is often unsuccessful in restoring endocrine function to normal. However, medical therapy with bromocriptine, a dopamine agonist, not only suppresses PRL levels, but may also lead to a reduction in tumor size. Previous reports have demonstrated radiographic evidence of tumor regression only after 3 or more months of bromocriptine therapy. We have now documented, for the first time, objective evidence of extremely rapid reduction in tumor size in two patients harboring large PRL-secreting pituitary tumors (mean pretreatment serum PRL levels, 2350 and 3900 ng/ml) who were prospectively treated with bromocriptine (7.5 mg/day) in preference to surgical intervention despite marked visual impairment in one of the patients. After 2 and 6 weeks of therapy, respectively, marked reduction in tumor size was demonstrated radiographically in both patients. Headache, visual acuity, and visual fields had improved after only 3 days. Although the mechanism of bromocriptine's antitumor activity is unclear, we believe that a large prospective trial to study the effects of bromocriptine therapy on the size of PRL-secreting macroadenomas is urgently needed to determine whether medical therapy should become the primary modality of treatment to reduce tumor size as well as restore endocrine function.

Adenoma↗
PubMed1980

[3H]3-O-methyl-D-glucose transport from blood into the lumina of the seminiferous and epididymal tubules in intact and vasectomized hamsters.

The investigation demonstrated a restriction of [3H]3-O-methyl-D-glucose ([3H]3-OMG) net transport into seminiferous tubule fluid. Net transport of [3H]3-OMG into the cauda epididymidal tubule was even more limited. By 4 months after vasectomy, there was no statistical difference in the net transport of the isotope into the seminiferous tubule fluid, but there was a significant increase in net transport into cauda epididymidal fluid. These results demonstrate that the blood-epididymal barrier can be even more restrictive to molecular transport than the blood-testis barrier and that vasectomy can have subtle effects on characteristics of molecular transport in the cauda epididymidis.

Animals↗
PubMed1980

Vasovasotomy.

Explore the source record for details and available documents.

Humans↗
PubMed1979

Effects of vasectomy on the blood-testis barrier of the hamster.

The effects of vasectomy on the blood-testis and blood-epididymal barriers to 3H2O, [3H]inulin, and [14C]urea were examined by study of the radioactivity appearing in micropuncture samples of fluids from the seminiferous tubules and cauda epididymidis. By 4 months after vasectomy, there were changes in the blood-seminiferous tubule barrier to [3H]water and [14C]urea (increased entry) and in the blood-epididymal barrier to [3H]water and [3H]inulin (increased entry) and to [14C]urea (decreased entry). These subtle changes could have an impact on spermatogenesis and/or sperm maturation after vasectomy.

Animals↗
PubMed1979

The effects of vasectomy on testicular metabolism in the guinea-pig.

The effects of vasectomy on testicular DNA production were studied in guinea-pigs at 2 weeks and 2 and 6 months after surgery. By 6 months, vasectomy had resulted in lower testicular weight and absolute DNA, RNA and protein contents, although RNA and DNA concentrations/protein were unchanged. Incorporation of thymidine into the testis had decreased by 2 weeks after vasectomy, and continued to do so unless the ductal system subsequently ruptured and formed a granuloma when thymidine incorporation returned to normal control levels. It is suggested that in the guinea=pig vasectomy alters spermatogenesis by reducing testicular DNA synthesis.

Animals↗