Shinsuke Sasaki

Evidence that intravenous administration of interleukin-1 stimulates corticotropin releasing hormone secretion in the median eminence of freely moving rats: estimation by push-pull perfusion.

Utilizing push-pull perfusion, we examined secretory profiles of corticotropin releasing hormone (CRH) in the median eminence (ME) and of plasma adrenocorticotropin (ACTH) in freely moving male rats after intravenous bolus injection of recombinant human interleukin (IL)-1 alpha (1.0 microgram) and 1 beta (1.0 microgram). The ME was perfused with artificial cerebrospinal fluid between 11.00 and 14.00 h, and perfusates and blood samples were collected every 20 min. Administrations at 12.00 h of IL-1 alpha and 1 beta, but not vehicle only, resulted in significant increases in both the plasma ACTH and ME-CRH. The rise in ME-CRH clearly preceded the enhanced ACTH secretion. These in vivo data strongly suggest that IL-1 stimulates ACTH secretion, at least in part, by triggering hypothalamic CRH release. This is the first to characterize the temporal profile of CRH secretion in the ME after intravenous administration of IL-1 to freely moving rats.

Involvement of Oxytocin and Cholecystokinin-8 in lnterleukin-1β-Induced Adrenocorticotropin Secretion in the Rat

It is well established that corticotropin-releasing hormone (CRH) is a principal neuropeptide which mediates the adrenocorticotropic hormone (ACTH) secretory response to interleukin (IL)-1 in the rat. It has recently been suggested that besides CRH, arginine vasopressin may also play a stimulatory role in IL-1 induced ACTH secretion. However, it remains to be elucidated whether other neuropeptides possessing an ACTH-releasing activity are involved in this neuroendocrine event. Therefore, in this study, we examined possible roles for oxytocin (OT) and cholecystokinin (CCK)-8 in the IL-1-induced ACTH response, utilizing the technique of immunoneutralization of these peptides. For comparison, we examined the effect of CRH immunoneutralization as well. Human recombinant IL-1 beta (50 ng) was given intracerebroventricularly (to the 3rd ventricle) to freely moving male rats 15 min after injecting specific antiserum against CRH, OT, or CCK-8, or normal rabbit serum (control) via the same route. As expected, anti-CRH antibody significantly suppressed the ACTH response to IL-1 beta. Interestingly, anti-OT antibody acted in the same manner, whereas anti-CCK-8 antibody did not. These results suggest that in addition to CRH and arginine vasopressin, OT may also play a significant role in mediating the IL-1 beta-induced ACTH secretion in the rat.

The Role of Arginine Vasopressin in Interleukin-1β Induced Adrenocorticotropin Secretion in the Rat

In this study we examined whether arginine vasopressin (AVP) in the brain is involved in the adrenocorticotropin (ACTH) secretion induced by interleukin (IL)-1 beta in the rat. Human recombinant IL-1 beta (50 ng) was given intracerebroventricularly to freely moving male rats with or without a prior (15 min before) administration of anticorticotropin releasing hormone (CRH) or AVP antibody via the same route. The ACTH response to IL-1 beta was significantly reduced by both anti-CRH and anti-AVP antisera compared to the levels after normal rabbit serum. These results suggest that not only CRH but also AVP may mediate the IL-1 beta stimulation of ACTH secretion in the rat.

Contradictory clinical implications between paradoxical growth hormone responses to thyrotropin-releasing hormone and those to vasoactive intestinal peptide and luteinizing hormone-releasing hormone in acromegaly

There is an almost general agreement on the clinical significance of TRH and bromocriptine (Br) tests in acromegaly. That is that positive GH responses to these tests (with an increase or a decrease, respectively) are known to be very frequently associated with the presence of PRL-containing somatotroph adenomas of the pituitary. In this context, however, very little is known about the clinical significance of paradoxical GH responses to vasoactive intestinal peptide (VIP) and LHRH in acromegaly. We therefore examined, as the principal objective of this study, whether a relationship exists among the GH (in some cases also PRL) responses to TRH, VIP, LHRH and Br in acromegaly. Another aim of this study was to examine whether a sexual difference exists in GH and PRL secretion in acromegaly. We examined a total of 24 patients comprising 8 men and 16 women. In agreement with previous reports, TRH-responders tended to have a higher level of basal PRL than TRH-nonresponders. In contrast, VIP-responders and LHRH-responders tended to have a lower PRL level than their respective counterparts. Although Br responsiveness was unexpectedly similar between TRH-responders and nonresponders, it was revealed that pure TRH-responders who were not responsive to VIP or LHRH were more sensitive to Br and more hyperprolactinemic than the remaining TRH-responders. This suggests that the simultaneous GH responsivity to VIP and/or LHRH in TRH-responders may be a factor which lowers their Br responsiveness and basal PRL levels. With respect to a sexual difference in GH and PRL secretion, it was revealed that female acromegalics had higher levels of basal GH and PRL than male patients. In addition, it was found that female acromegalics had supernormal levels of basal PRL, but a subnormal PRL responsiveness to TRH. As the major implication of this study, we hypothesize that the positive GH response to TRH associated with a high sensitivity to Br may, as already suggested, be characteristic of PRL-containing somatotroph adenomas, whereas the GH responsivity to VIP, and possibly also to LHRH, co-existing with no or low sensitivity to Br may be a feature of pure somatotroph adenomas. Although this study is devoid of immunohistochemical evidence to support this hypothesis, we suggest that the present in vivo data may be of some help in understanding the basis of the great variabilities in the GH responses to various dynamic testings in acromegaly.

A comparative study of the effects of neonatal androgenization and estrogenization on prolactin secretion in adult female rats

Effects of neonatal androgenization (NA) and estrogenization (NE) were compared especially in terms of the prolactin (PRL) secretion in female rats. Twenty-four h after birth, a total of seven groups of newborn female rats were treated as follows. Three NA groups received a single s.c. injection of 10, 100 or 1000 micrograms of testosterone, respectively. Similarly, three NE groups received 1, 10 or 100 micrograms of estradiol-17 beta, respectively. The remaining one group was injected with oil vehicle only, and served as controls. At 8 weeks of age, animals were killed by rapid decapitation. PRL, estradiol and progesterone were measured in the plasma. Anterior pituitary (AP) was weighed, and AP PRL content was measured. NA and NE, at the highest doses, resulted in a similar degree of hyperprolactinemia and hyperestrogenemia showing an effect ratio of about 1:10. This ratio was, however, not true with the lower doses. Furthermore, there was no dose-dependency in the effect of NE on the plasma PRL and estradiol levels. In turn, plasma progesterone levels were dose-dependently decreased by both NA and NE. AP PRL content, expressed per AP, was significantly higher than control values in only NA (1000 micrograms) and NE (100 micrograms) groups. AP weight was increased by NA (1000 micrograms) but not by any NE treatment. These results indicate that NA and NE do not always exert similar effects on the PRL secretion or on several other related parameters. Therefore, aromatization of testosterone to estradiol does not appear to be the sole mechanism mediating the neuroendocrine consequences of NA.

Vasoactive intestinal peptide levels in the hypothalamus and anterior pituitary do not change in association with the pre-ovulatory prolactin surge in the rat

We examined whether vasoactive intestinal peptide (VIP) is involved in the preovulatory prolactin (PRL) surge in the rat. Ovariectomized adult rats implanted sc with an estradiol capsule 2 days previously were decapitated at hourly intervals between 1100-1800 h. The plasma PRL and luteinizing hormone showed an evident surge at 1700 h and 1800 h, respectively. The anterior pituitary PRL content was significantly lower at and after 1600 h than at 1100 h. However, there was no significant change in the VIP content in the suprachiasmatic nucleus, paraventricular nucleus, median eminence or anterior pituitary throughout the entire period of observation. Since all of these regions are known to be involved in the VIP synthesis and/or release, the present results appear to cast some doubt on previous studies reporting a significant role for VIP in the generation of the pre-ovulatory PRL surge.

Neonatal androgenization increases vasoactive intestinal peptide levels in rat anterior pituitary: possible involvement of vasoactive intestinal peptide in the neonatal androgenization-induced hyperprolactinemia

Accumulating evidence suggests that vasoactive intestinal peptide (VIP) may be a physiological PRL-releasing factor. In the present study, we examined a possible involvement of VIP in the neonatal androgenization (NA)-induced hyperprolactinemia. Twenty-four hours after birth, newborn female rats were injected sc with 1,000 µg of testosterone (NA) or with oil vehicle only (control). Both groups were sacrificed at 8 weeks of age. Compared to controls, NA rats showed significantly higher plasma PRL levels (7.3 fold), anterior pituitary (AP) PRL content (2.1 fold) and plasma estradiol levels (2.1 fold). AP VIP content was extremely higher (61 fold) in NA rats than in controls. However, NA did not affect VIP content in the suprachiasmatic nucleus, paraventricular nucleus or median eminence. These results suggest that the NA-induced hyperprolactinemia may be mediated, at least in part, by paracrine and/or autocrine effects of the increased AP VIP on PRL secretion. However, since the potentiation by NA of the AP VIP content was extremely marked compared to those of the other parameters, the possibility was also raised that the increased AP VIP may be involved in other endocrine and/or nonendocrine events occurring in the AP.