To investigate the role of androgen receptors in the regulation of brain aromatase activity (AA) in adult rats, the levels of AA in discrete brain areas of androgen-insensitive testicular feminized (Tfm) rats were compared with those in their normal male littermates (NL). AA was measured in homogenates of brain tissue by using a radiometric assay that quantifies the production of 3H2O from [1 beta-3H]androstenedione as an index of estrogen formation. Initially, we assessed the capability of block-dissected tissues to aromatize androgens. We found that the AA in the amygdala and hypothalamus-preoptic area of Tfm rats was significantly lower (P less than 0.001) than the AA in NL despite the fact that circulating androgen concentrations in the Tfm were significantly higher. Kinetics studies demonstrated that the apparent Michaelis constant was equivalent for both groups (0.02-0.03 microM). Administration of testosterone propionate to castrated males produced 3 to 4-fold elevations of AA in NL, but did not affect brain AA in Tfm rats. To pinpoint specific sites where AA is affected in Tfm rats, we measured AA in 10 hypothalamic and limbic nuclei that were dissected from 300-micron frozen brain sections. Compared to NL, Tfm rats exhibited significantly lower levels of AA in all micro-dissected brain regions studied, except for the medial and cortical amygdala. These data provide genetic evidence for both androgen-dependent and independent regulation of AA in the rat brain.

Our laboratory has shown that the Y chromosome has a significant effect on blood pressure in the spontaneously hypertensive rat (SHR) model of hypertension and that the testes and androgen receptor contribute to the blood pressure rise. As an extension of our research, we have developed two new rat strains, SHR/a and SHR/y (F u ) to study the Y chromosome. The objectives of the following research were 1) to study the blood pressure of rats with an SHR Y chromosome in a normotensive genetic background (SHR/y) or a normotensive Y chromosome in an SHR genetic background (SHR/a), 2) to determine the effect of male sex phenotype on the blood pressure of these rats, 3) to determine if testosterone replacement in castrated rats would restore blood pressure, and 4) to determine whether the Y chromosome from the SHR/y strain when crossed with a normotensive female can induce hypertension in androgen receptor-deficient male offspring. Blood pressure of male SHR/y rats was significantly higher than that of normotensive Wistar-Kyoto males (p<0.01), and SHR/a males had significantly lower blood pressure compared with that of the parent SHR strain (p=0.05). Testosterone replacement in castrated rats of both strains (SHR/a and SHR/y) restored blood pressure to control levels. Normotensive female King-Holtzman rats heterozygous for the testicular feminization gene were crossed with F n SHR/a and SHR/y males. The F, males (King-Holtzman female x SHR/a male) with normal androgen receptor and hypertensive autosomes had a final blood pressure of 155 mm Hg compared with 175 mm Hg (/?<0.01) for their counterparts -F, males (King-Holtzman female x SHR/y male) with normal androgen receptor and a Y chromosome from hypertensive fathers. Testicular feminized rats that lacked the androgen receptor and females from both crosses had a similar blood pressure of 125-130 mm Hg. In conclusion, the hypertensive Y chromosome increased blood pressure after backcrossing (F n ) into a normotensive autosomal background and increased blood pressure by 20 mm Hg more than the hypertensive autosomes in a normotensive background. Also, the Y chromosome and autosome effects both appear to require testosterone and the androgen receptor for maximal effect (Hypertension 1993^1:1071(Hypertension 1993^1: -1075 KEY WORDS • Y chromosome • genetics • receptors, androgen • testicular feminization • rat S ex differences in blood pressure (BP) have been reported in most developed societies and in most animal studies, with males having higher pressures than females.1 -6 Recently, our laboratory has shown that the Y chromosome has a significant effect on BP in the spontaneously hypertensive rat (SHR) model of hypertension 7 -8 and in a new hybrid rat model of hypertension that also implicates an androgen receptor (AR) component. 9To study the Y chromosome effects, we have developed two new rat substrains: SHR/a and SHR/y. F n males of SHR/y have 99.9% of their autosomes and X chromosome from a Wistar-Kyoto (WKY) rat and a Y chromosome from an SHR father; F n males of SH...

We noninvasively monitored the partial pressure of oxygen (pO2) in rat small intestine using a model of chronic mesenteric ischemia by electron paramagnetic resonance oximetry (EPR) over a 7-day period. The particulate probe lithium octa-n-butoxynaphthalocyanine (LiNc-BuO) was embedded into the oxygen permeable material polydimethyl siloxane (PDMS) by cast-molding and polymerization (Oxy-Chip). A one-time surgical procedure was performed to place the Oxy-Chip on the outer wall of the small intestine (SI). The superior mesenteric artery (SMA) was banded to approximately 30% blood flow for experimental rats. Noninvasive measurement of pO2 was performed at baseline for control rats or immediate post-banding and on days 1, 3, and 7. The SI pO2 for control rats remained stable over the 7-day period. The pO2 on day 7 was 54.5 ± 0.9 mmHg (mean ± SE). SMA banded rats were significantly different from controls with a noted reduction in pO2 post banding with a progressive decline to a final pO2 of 20.9 ± 4.5 mmHg (mean ± SE; p = 0.02). All SMA-banded rats developed adhesions around the Oxy-Chip yet remained asymptomatic. The hypoxia marker Hypoxyprobe™ was used to validate low tissue pO2. Brown cytoplasmic staining was consistent with hypoxia. Mild brown staining was noted predominantly on the villus tips in control animals. SMA-banded rats had an extended region of hypoxic involvement in the villus with a higher intensity of cytoplasmic staining. Deep brown staining of the enteric nervous system neurons and connective tissue both within layers and in the mesentery were noted. SMA banded rats with lower pO2 values had a higher intensity of staining. Thus, monitoring SI pO2 using the probe Oxy-Chip provides a valid measure of tissue oxygenation. Tracking pO2 in conditions that produce chronic mesenteric ischemia will contribute to our understanding of intestinal tissue oxygenation and how changes impact symptom evolution and the trajectory of chronic disease.

Rat pups were hemicastrated and uptake of [3H] thymidine by Sertoli cells in the remaining testis was compared to that in testes of sham-operated pups at intervals of from 8 h to 21 days after surgery. Labeled thymidine was administered subcutaneously 2 h before sacrifice. Testes were processed for light microscope autoradiography and the percent of Sertoli cell nuclei that had incorporated [3H] thymidine was determined by scoring nuclei in tissue sections as labeled or unlabeled. The percentage of cells labeled was increased in hemicastrates over intact controls by 8 h after surgery and testicular hypertrophy became apparent in hemicastrates by the following day. Labeling of Sertoli cells in hemicastrates remained elevated for 4 days and then returned to normal. When plasma levels of gonadotropins were measured in both groups 4 days after surgery, follicle-stimulating hormone (FSH) was found to be more than twice normal in hemicastrates while luteinizing hormone (LH) was unchanged. The effect of testosterone on the response of Sertoli cells to hemicastration was also examined. In hemicastrates, 2 days of androgen therapy depressed, and an additional 2 days abolished, the proliferative response of the Sertoli cells. Our findings suggest that increased proliferation of Sertoli cells within the remaining testis is involved in the enlargement of the testis that follows hemicastration. They also imply that prevention of compensatory hypertrophy by testosterone involves interference with this response of Sertoli cells in some way. Finally, our data implicate FSH in control of Sertoli cell proliferation in vivo in immature rats.