Neonatal castration affects intrathymic kinetics of T-cell differentiation and the spleen T-cell level

To test putative interdependence in the ontogenesis of the hypothalamic-pituitary-gonadal and thymic-lymphatic axes, thymocyte differentiation and maturation was examined in neonatally castrated (Cx) adult rats. In the hypercellular thymi of Cx rats, the proportion of the least mature CD4(-)CD8(-)TCRalphabeta(-) triple negative (TN) thymocytes was reduced, while the proportions of all downstream double positive (DP) subsets (TCRalphabeta(-), TCRalphabeta(low) and TCRalphabeta(high)) were increased when compared with neonatally sham-castrated (Sx) adult rats. This suggested an accelerated thymocyte transition from the TN to DP TCRalphabeta(low) developmental stage accompanied by an increased positive/ reduced negative thymocyte selection. The increased thymocyte surface density of Thy-1, which is implicated in thymocyte hyposensitivity to negative selection, in Cx rats further supports the previous assumption. The finding that the proportions of both single positive (SP) TCRalphabeta(high) thymocyte subsets were reduced, while their numbers were increased (CD4(+)CD8(-)) or unaltered (CD4(-)CD8(+)), coupled with results demonstrating an increased level of CD4(-)CD8(+) cells without changes in that of CD4(+)8(-) cells in the spleen indicate: (i) accelerated differentiation and maturation of the positively selected DP TCRalphabeta(high) thymocytes towards CD4(-)8(+) TCRalphabeta(high) cells followed by increased emigration of the mature cells and (ii) decelerated differentiation and maturation towards CD4(+)8(-)TCRalphabeta(high) cells in Cx rats. Furthermore, the unaltered proportion of intrathymically developing CD4(+)CD25(+)Foxp3(+) regulatory cells in Cx rats, in light of putative hyposensitivity of thymocytes to negative selection suggesting reduced elimination of autoreactive cells, may provide a firm basis for understanding the reasons behind increased susceptibility of Cx rats to autoimmune disease induction.

Colonic vasoactive intestinal polypeptide (VIP) in ulcerative colitis--a radioimmunoassay and immunohistochemical study

BACKGROUND/AIMS

In this study, we present radioimmunoassay data describing the concentration of Vasoactive Intestinal Polypeptide (VIP) in both plasma and colonic biopsies, as well as immunostaining of VIPergic innervation in mucosal biopsies of normal subjects and patients with ulcerative colitis (UC).

PATIENTS AND METHODS

Thirty three patients with UC and 17 healthy subjects were investigated. All UC patients suffered from active disease. Fasting circulating levels of VIP in plasma as well as tissue concentrations were measured by radioimmunoassay. For the immunohistochemistry, polyclonal antibody against VIP and the streptavidin-biotin peroxidase complex technique were carried out.

RESULTS

Overall plasma VIP concentrations in the UC patients were similar to those in the controls. Significantly decreased concentrations of VIP were found in UC of rectum compared to the normal tissue. However, both plasma VIP values and tissue concentrations were found to be significantly lower in patients expressing minimal or mild active disease according to clinical activity index (AI) and histological activity index (HAI), but marked increase of plasma VIP was clear in UC patients with moderate or severe AI and HAI. There was a trend towards increased tissue concentrations of VIP in the group of patients with moderate or severe AI and HAI. Our immunohistochemical analysis of VIP fibers and nerve cell bodies revealed consistently weaker VIP-immunoreactivity in the rectum in UC patients with minimal or mild HAI. Simultaneously, in the rectal biopsies from UC patients with moderate and severe disease, the fibers in the lamina propria and ganglion cells in the submucous plexus were markedly increased in density and in degree of immunostaining. Very strong immunoreactivity was also found in inflammatory cells of the lamina propria as well as in the epithelial layer of the biopsies from UC patients with obvious disease.

CONCLUSIONS

Our study shows clearly the heterogeneity in the response of VIP plasma level as well as rectum concentration and distribution in UC patients at different stages of the active disease. The possible role of VIP in the colon suggests that further studies of the alterations of this gut peptide may be useful in the understanding of UC pathophysiology.

Stereological analysis of the sexually mature rat thymus after orchidectomy

To assess the significance of gonadal function in the maintenance of thymic structure, male, sexually mature, 60 days old rats were bilaterally orchidectomized and the volumes of both the thymic compartments, total cellularity of each of them, as well as density (Nv) and mean diameter (D) of thymocytes within the specific thymic regions were stereologically analyzed 3, 7 and 15 days later. Three days after the orchidectomy a decrease in the thymic weight, and a reduction of both the cortical and medullary volumes, were observed. The reduction in cortical volume was followed by a decrease in overall number of the cortical thymocytes, suggesting an enhanced process of thymocyte death. In the same animals, the total number of the medullary thymocytes as well as D remained unchanged. Seven days after orchidectomy both volume of the cortex and total number of the cortical thymocytes reached the control values, while all the changes observed in the medulla of rats 3 days post castration, persisted. In addition, 7 days post castration, the volume of the interlobular connective tissue was increased and this persisted at day 15 post castration. The results indicate that orchidectomy can affect the thymic structure, and possibly the process of intrathymic T cell maturation; the extent of changes depending on the duration of the gonadal deprivation.

Prepubertal castration alters the phenotypic profile of adult rat thymocytes

To assess the gonadal influence on the maturation of the thymus, rats were orchidectomized at different periods critical for programming of both gonadal and immune functions, and the composition of the intrathymic thymocyte population was determined in adults by flow cytometric analysis of the surface phenotype. The relative proportion of thymocytes expressing CD4, CD8 and T cell receptor (TCR)alpha beta was measured in the adult rats castrated at 1, 7 and 30 days. Castration performed at postnatal day 1 did not significantly affect expression of these molecules. However, in rats subjected to the surgery at day 7, a significant decrease in the proportion of CD4+CD8+ double-positive cells was found, in parallel with a proportional increase in the percentage of CD4+CD8- single-positive (SP) cells. In rats castrated at age 30 days, in addition to these changes, a small but significant increase in the percentage of CD4-CD8+ SP thymocytes was measured. Castration performed at age 7 and 30 days also caused an enrichment in the thymocyte population expressing TCR alpha beta, probably related to the increase of CD4+CD8- SP cells (7 days) and both CD4+CD8- and CD4-CD8+ SP cells (30 days). The total yield of thymocytes was increased in all experimental groups. We conclude that T cell maturation sequences in the adult thymus are altered if gonadal influence is removed during certain stages of thymus development.

In vivo and in vitro studies on the opioidergic control of the secretion of gonadotrophin-releasing hormone and luteinizing hormone in sexually immature and adult male rats

In vivo and in vitro methods have been used to compare the effects of opioid receptor blockade on the functional activity of the hypothalamo-pituitary-gonadal axis in adult (200 g) and sexually immature (50 g) male rats. In the adult, a single injection of the mu-receptor antagonist, naloxone (500 micrograms/100 g body weight, s.c.), produced hypersecretions of luteinizing hormone (LH) and testosterone. Maximal serum concentrations of the two hormones were attained within 20 and 60 min respectively. In contrast, neither ICI 174864 (100 micrograms/100 g body weight, s.c.) nor MR2266 (150 micrograms/100 g body weight, s.c.), which block delta- and kappa-receptors respectively, stimulated pituitary-gonadal activity; indeed, like the saline vehicle, both tended to depress the serum LH concentration. The injection procedure was sufficient to activate the hypothalamo-pituitary-adrenal axis and, thus, the vehicle-treated controls exhibited significant increases in the plasma adrenocorticotrophin and serum corticosterone concentrations. These effects were enhanced by naloxone (500 micrograms/100 g body weight, s.c.) and by the kappa-opioid receptor (MR2266, 150 micrograms/100 g body weight, s.c.) but not by the delta-opioid receptor antagonist (ICI 174864, 30-100 micrograms/100 g body weight, s.c.). The increases in serum corticosterone and LH concentration induced by naloxone in adult rats were not apparent in the sexually immature (50 g) animals. To the contrary, in the young rats naloxone (250 and 500 micrograms/100 micrograms body weight, s.c.) attenuated, in a dose-dependent manner, the pronounced hypersecretion of corticosterone induced by the vehicle injection. The higher dose of the antagonist (500 micrograms/100 g body weight, s.c.) also overcame the significant reductions in serum LH evident 20 (p less than 0.05) and 40 (p less than 0.01) min after the saline injection but the lower dose (250 micrograms/100 g body weight, s.c.) was ineffective in this respect. In vitro, hypothalami from both adult and sexually immature rats responded to the addition of naloxone (10(-8)-10(-6) M) to the incubation medium with significant (p less than 0.01) concentration-dependent increases in the release of gonadotrophin-releasing hormone (GnRH). In contrast, ICI 174864 (10(-7)-10(-6) M) and MR2266 (10(-7)-10(-6) M) had little effect on the secretion of the releasing hormone by hypothalami from rats of either group although, at the highest concentration tested, MR2266 (10(-6) M) precipitated a small increase in GnRH release from hypothalami from adult rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Peripubertal changes in the nature of the GnRH response to alpha-adrenoceptor stimulation in vitro and their modulation by testosterone

Adrenergic mechanisms have been widely implicated in the regulation of GnRH secretion in adult rats but their role in young animals, in which the activity of the GnRH neurones is minimal, is unclear. These experiments were done to examine the effects of alpha-adrenoceptor stimulation on the secretion in vitro of GnRH by hypothalami from immature and adult male rats. The alpha 1-adrenoceptor agonist, phenylephrine (10(-9) - 10(-7) M), stimulated release of GnRH from hypothalami from adult (200 g) and peripubertal (150 g) rats but inhibited markedly the secretion of the releasing factor from the limited stores available in hypothalami from immature (50 or 100 g) rats. The stimulatory and inhibitory responses to phenylephrine, evident in adult and younger rats respectively, were concentration-dependent and antagonized readily by the selective alpha 1-adrenoceptor antagonist, alfuzosin (10(-6) M), but not by the beta-adrenoceptor antagonist, propranolol (10(-6) M). Hypothalami from 14-day castrated adult rats, in which the serum LH was elevated and hypothalamic GnRH content reduced, responded to alpha 1-adrenoceptor stimulation in vitro, like those from immature rats, with a marked reduction in GnRH release. In contrast, hypothalami from corresponding castrates bearing testosterone implants, which maintained the hypothalamic GnRH content and serum LH and testosterone concentrations at levels similar to those of intact controls, exhibited the normal 'adult' response to phenylephrine. Studies utilizing 3H-prazosin indicated that the number (Bmax) of hypothalamic alpha 1-adrenoceptor binding sites increases at puberty but that receptor affinity (KD) is unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)