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PubMed1999

Transnasal transsphenoidal hypophysectomy: choice of approach for the otolaryngologist.

Increasingly, the otolaryngologist is called on to provide exposure for the neurosurgeon performing transsphenoidal hypophysectomy. The 3 most common approaches for this exposure are the transnasal transseptal, sublabial transseptal, and external rhinoplasty approaches. We reviewed our series of 135 patients undergoing transnasal hypophysectomy for postoperative complications. In our series, we found that 18% of patients had a postoperative septal perforation, 2% of which were symptomatic; 6% of patients reported nasal cosmetic deformity; 13% reported transient lip numbness; and 3% reported postoperative nasal dysfunction. When comparing our complication rate with those published for the sublabial and external rhinoplasty approaches, we found the transnasal approach provides excellent exposure with less dissection and fewer postoperative complications. On the basis of these results, we believe that the transnasal transseptal approach provides excellent exposure for transsphenoidal hypophysectomy in all patients who require pituitary surgery.

Adult↗

PubMed2001

Hypophysectomy as a treatment for canine and feline Cushing's disease.

The microsurgical technique of transsphenoidal hypophysectomy performed with the dogs and cats positioned in sternal recumbency enables the treatment of Cushing's disease, independent of skull type, in a safe and effective manner. In dogs, the short-term survival rate after hypophysectomy is comparable to that after treatment with o,p'-DDD, whereas the recurrence rate in this period is lower. When the surgeon has gone through a learning curve, the results of the 1- to 3-year follow-up interval may be better than those after adrenocorticolysis with o,p'-DDD. CT enables assessment of localization and size of the pituitary before surgery. In general, dogs with Cushing's disease and normal-sized pituitaries or moderately enlarged pituitaries (up to 12 mm in diameter) are suitable candidates for transsphenoidal surgery. In dogs with larger pituitary tumors and tumor extension rostrally or caudally over the dorsum sellae, transsphenoidal debulking surgery may be only a palliative treatment. The main complications are postoperative hypernatremia, keratoconjunctivitis sicca, diabetes insipidus, and secondary hypothyroidism. In cats, special attention should be paid to closure of the soft palate. The neurosurgeon must be familiar with these complications so as to recognize them as early as possible and to treat them immediately and effectively. It is concluded that microsurgical transsphenoidal hypophysectomy in dogs and cats with Cushing's disease is an effective method of treatment.

Animals↗

PubMed1967

Changes in the enzyme pattern of the mammary gland of the lactating rat after hypophysectomy and weaning.

1. The enzymes glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphoglucomutase, UDP-glucose pyrophosphorylase, phosphofructokinase, ATP-citrate lyase and acetyl-CoA carboxylase have been assayed in rat mammary glands in various stages of involution after hypophysectomy and weaning. 2. After hypophysectomy all seven enzymes decline in activity over a 12-16hr. period but the extent of the decline varies, with acetyl-CoA carboxylase becoming almost totally inactive, ATP-citrate lyase and phosphofructokinase showing a large decrease, and the remaining enzymes a less marked decline. 3. Within 24hr. of removing the litter a change in the pattern of enzyme activity is found very similar to that after hypophysectomy. 4. The significance of these results is discussed in relation to the endocrine control of mammary gland metabolism and the mechanisms of involution.

Animals↗

PubMed1979

Effect of hypophysectomy on the rates of protein synthesis and degradation in rat liver.

The effect of hypophysectomy on the protein metabolism of the liver in vivo was studied. Fractional rates of protein synthesis and degradation were determined in the livers of normal and hypophysectomized rats. Synthesis was measured after the injection of massive amounts of radioactive leucine. Degradation was estimated either as the balance between synthesis and accumulation of stable liver proteins or from the disappearance of radioactivity from the proteins previously labelled by the injection of NaH14CO3. The results indicate that: (1) hypophysectomy diminishes the capacity of the liver to synthesize proteins in vivo, mainly of those that are exported as plasma proteins; (2) livers of both normal and hypophysectomized rats show identical protein-degradation rates, whereas plasma proteins are degraded slowly after hypophysectomy.

Animals↗

PubMed1988

Effect of age, gonadectomy and hypophysectomy on mitochondrial hydroxylation of vitamin D3 (cholecalciferol) and of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol in female and male rat liver.

In a previous study we found that liver mitochondrial side-chain hydroxylation of vitamin D3 (cholecalciferol) and of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol was higher in female than in male rats [Saarem & Pedersen (1987) Biochem. J. 247, 73-78]. The present paper describes the effects of age, gonadectomy and hypophysectomy on these activities. The sex difference became manifest above the age of 7 weeks. Ovariectomy and/or injection of oestradiol valerate had no effect on the hydroxylase activities in adult females. Castration increased, and subsequent testosterone treatment decreased, the hydroxylase activities in adult males. Hypophysectomy had no effect in females, but increased the hydroxylase activities in males. Testosterone treatment had no effect in hypophysectomized females or males. Injection of oestradiol valerate had no effect on the hydroxylase activities in hypophysectomized females. In hypophysectomized males this treatment had no effect on the vitamin D3 25-hydroxylase activity, but decreased the C27-steroid 27-hydroxylase activity in males. Microsomal 1 alpha-hydroxyvitamin D3 25-hydroxylase activity was lower in females than in males in all age groups. Castration or hypophysectomy decreased the activity in male rats. It is concluded that, in adult female rats, the mitochondrial side-chain hydroxylation of vitamin D3 and of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol is independent of sex hormones. In males these activities are regulated by influence of sex hormones on the hypophysis, probably by the presence of androgens in the neonatal period. Different effects on the two hydroxylases indicate the presence of at least two different cytochromes P-450 in rat liver mitochondria.

Aging↗

PubMed1990

Increase in the amount of glutathione transferase 4-4 in the rat adrenal gland after hypophysectomy and down-regulation by subsequent treatment with adrenocorticotrophic hormone.

The effect of hypophysectomy and subsequent treatment with adrenocorticotropic hormone (adrenocorticotropin, ACTH) on the isoenzymes of glutathione transferase in the rat adrenal gland was investigated. A large increase (approx. 11-fold) in the level of transferase subunit 4 was observed in hypophysectomized animals by immunoblotting. When the activity of glutathione transferase 4-4 was measured in adrenal cytosol using trans-stilbene oxide as a selective substrate, a 15-fold increase was noted. Lack of the pituitary hormone ACTH is apparently related to this increase, since treatment of hypophysectomized animals with ACTH for 2 weeks partially down-regulated subunit 4. Glutathione transferase subunits 3 and 8 in the adrenal were also increased in amount by hypophysectomy, but not at all to the same extent. The activity of glutathione transferase 4-4 was elevated also in the liver and ovary (5 and 1.5 times respectively) after hypophysectomy. These elevated enzyme levels were, however, not affected by ACTH treatment. This down-regulation of glutathione transferases in the rat adrenal by ACTH may be related to the fact that, under normal conditions, this organ is highly susceptible to the toxic effects of various polycyclic hydrocarbons, whereas under circumstances where there is no ACTH production, as in hypophysectomized rats, the adrenal is resistant to these same hydrocarbons.

Adrenal Glands↗

PubMed1997

A comparison of the insulin tolerance/glucagon test with the short ACTH stimulation test in the assessment of the hypothalamo-pituitary-adrenal axis in the early post-operative period after hypophysectomy.

OBJECTIVE: The insulin tolerance test (ITT) is the established reference test for assessing the hypothalamo-pituitary-adrenal (HPA) axis. Various authorities, however, have suggested that the 250 microgram short ACTH stimulation test may be used to assess the HPA axis in place of the ITT in suspected hypopituitarism, although a number of other studies have suggested that the test may be unreliable in this setting. In this study, the ITT (or glucagon test) has been compared with the 250 microgram short ACTH stimulation test in patients with pituitary tumours pre-operatively and within 2 weeks of trans-sphenoidal hypophysectomy. DESIGN: An ITT, or a glucagon test when the ITT was contraindicated, and the 250 micrograms short ACTH stimulation test, were performed in all the patients before (an ITT in 18 and a glucagon test in three patients) and within 2 weeks after trans-sphenoidal hypophysectomy (an ITT in 16 and a glucagon test in five patients). PATIENTS: Twenty-one patients with pituitary disorders (15 with acromegaly, one with a prolactinoma and five with non-functioning tumours) were studied; four had a microadenoma, two a mesoadenoma and 15 a macroadenoma. MEASUREMENTS: Serum cortisol was measured by radioimmunoassay. A normal response was defined as a rise in serum cortisol to 580 nmol/l or above for all the tests. RESULTS: Before surgery, three of 18 patients (17%) had a discrepancy between the ITT and the 30 minute short ACTH stimulation test and one of three between the glucagon test and the 30 minute short ACTH stimulation test. Combined together, pre-operatively, four of 21 patients (19%) had discrepant results. In the early post-operative period, the discrepancy between ITT and the 30 minute short ACTH stimulation test was higher with four of 16 patients (25%) showing discordant results; one of the five patients tested had a discrepancy between the glucagon test and the 30 minute short ACTH stimulation test. On combining the tests, the post-operative discrepancy was five of 21 patients (24%). CONCLUSIONS: The 250 microgram short ACTH stimulation test produces discordant results from the ITT in a clinically significant proportion of affected patients when assessing the HPA axis, although the rate of discordance varies according to the criteria used for normality for both the tests. We suggest that the ITT should remain the preferred test for assessing ACTH secretory capacity compared with the standard 250 microgram short ACTH stimulation test, both in the preoperative and in the early post-trans-sphenoidal hypophysectomy period.

Adenoma↗

PubMed1997

Changes in distribution of cystatin C, apolipoprotein E and ferritin in rat hypothalamus after hypophysectomy.

To clarify the mechanism underlying the process of degeneration of injured CNS neurons, we have immunohistochemically examined the distribution of cystatin C, apolipoprotein E, IgG, transferrin and ferritin in the hypophysectomized rat hypothalamus. Stainings for ferritin revealed that reactive microglial cells massed in the paraventricular and supraoptic nuclei 14 days after hypophysectomy, when the degeneration of vasopressin neuronal cell bodies was apparent. Cystatin C-positive magnocellular neurons first appeared at 4 days and the number of intensely-stained cells increased rapidly up to the 7th day of hypophysectomy, followed by a decrease thereafter. Most of such cystatin C-positive neurons were simultaneously stained with anti-vasopressin serum. Accumulation of apolipoprotein E in extracellular spaces was obvious in the both hypothalamic magnocellular nuclei at 7 days. Several apolipoprotein E-positive cells were localized in the supraoptic nucleus, although the number of apolipoprotein E-positive cells was much smaller than that of cystatin C-positive cells. The experiments performed with the transferrin and IgG antibodies showed undetectable levels of such molecules in and around the degenerating magnocellular neurons during whole experimental periods. These findings suggest the importance of cystatin C and apolipoprotein E in the process of degeneration and/or regeneration of magnocellular neurons after hypophysectomy.

Animals↗

PubMed1982

Influence of hypophysectomy and prolactin on the rat pinealocyte: a quantitative ultrastructural study.

The effects of hypophysectomy and prolactin administration on the ultrastructure of rat pinealocytes were studied by means of morphometric analysis. Hypophysectomy resulted in an increase in the Golgi apparatus and dense-core vesicles and a decrease in the granular endoplasmic reticulum, lysosomes and lipid droplets. Prolactin administration induced an increase in the granular endoplasmic reticulum and in the vacuoles which contained a flocculent material. Administration of prolactin to hypophysectomized rats raised the lowered levels of granular endoplasmic reticulum and lipid droplets to control values and caused an increase in vacuoles containing a flocculent material. Although hypophysectomy appeared to diminish the general activity of pinealocytes, it stimulated the neurosecretory-like secretory process Golgi apparatus-dense-core vesicles), whereas prolactin appeared to stimulate the ependymal-like secretory process (granular endoplasmic reticulum-vacuoles containing a flocculent material).

Animals↗

PubMed1976

Effect of hypophysectomy and insulin on lipogenesis in cockerels.

Hypophysectomy increases hepatic lipogenesis in cockerels. In an attempt to find the possible hormonal mechanism for this we have examined the effects of hypophysectomy, insulin and pituitary homogenates on hepatic lipogenesis. Insulin (5 U/kg) injected intravenously, simultaneously with glucose-14C tracer, increased the amount of 14C found in liver lipids at 30 min after the injection. Similarly, insulin injected 5 min before killing, increased the incorporation of glucose-14C and acetate-14C by liver slices during a 30 min incubation. Hypophysectomy increased lipogenesis within 24 hours. The effect of insulin was most pronounced in hypophysectomized cockerels. The activity of the lipogenic enzyme, acetyl CoA carboxylase was similarly affected. A homogenate of chicken pituitaries added to the medium reduced lipid synthesis from glucose-14C by liver slices. This effect was larger in liver slices in which lipogenesis had been stimulated by insulin. The increased rate of hepatic lipgenesis in hypophysectomized cockerels may be caused partly by increased hepatic sensitivity to the lipogenic action of insulin or by the removal of a direct inhibition by pituitary hormones.

Acetyl-CoA Carboxylase↗

PubMed1976

Effect of food deprivation and hypophysectomy on in vitro protein synthesis by membrain-bound and free hepatic ribosomes.

The protein synthetic activities of membrane-bound and free hepatic ribosomes isolated from intact rats fed ad libitum, and normal rats subjected to food restriction to match that of hypophysectomised (Hx) rats were compared to the in vitro protein synthetic capacity of hepatic ribosomes isolated from Hx rats. Hypophysectomy resulted in decreased protein synthetic ability of bound ribosomes, whether protein synthesis was directed by endogenous messenger RNA (mRNA) (p less than 0.05) or by polyuridylic acid (polyU) (p less than 0.01). In contrast, the protein synthetic activity of free hepatic ribosomes from Hx rats was reduced when protein synthesis was directed by endogenous mRNA (p less than 0.05) but, when polyU was substituted as the messenger, the protein synthetic activity of these free ribosomes was equal to that of control rats. On the other hand the effects of food restriction on hepatic ribosomal function could be clearly differentiated from the effects observed following hypophysectomy. Thus, the reduced protein synthetic activity of hepatic bound ribosomes isolated from food restricted normal rats was not demonstrable, when polyU was used to direct protein synthesis. Further, food restriction had no effect on the protein synthetic activity of free hepatic ribosomes, and this was true when protein synthesis was directed by either endogenous or artificial messenger. It is concluded that hypophysectomy reduces the protein synthetic ability of both bound and free hepatic ribosomes, and this change of ribosomal function of Hx rats cannot be attributed to their decreased food intake.

Animals↗

PubMed1992

ACTH immunoactivity in normal rat tissues: modulation by hypophysectomy and adrenalectomy.

This study investigates the effect of pertubation of the normal pituitary-adrenal axis on concentrations of adrenocorticotropin (ACTH)-like immunoactivity in peripheral tissues. We used a polyclonal antibody (West antibody) to measure ACTH-like immunoactivity in glacial acetic acid extracts of five tissues in adult male rats at increasing times (1, 7, 14, and 28 days) after hypophysectomy or adrenalectomy, and in normal control rats. Concentrations of ACTH-like immunoactivity were similar to those previously reported in liver, colon, heart, and small intestine and were not significantly affected by either hypophysectomy or adrenalectomy. While hypophysectomy also had no effect in the kidney, adrenalectomy resulted in a four-fold increase in extractable immunoactivity, first noticeable at seven days (p less than 0.005), but increasing progressively to 28 days (p less than 0.0005). Gel filtration showed that most of the increase in activity in kidneys of adrenalectomized rats corresponded to the 4.5 kD form comprising most of the serum ACTH immunoactivity and suggesting that the activity increase in kidney was largely due to ACTH derived from blood.

Adrenalectomy↗

PubMed1994

Metastatic behavior of the RIF-1 murine fibrosarcoma: inhibited by hypophysectomy and partially restored by growth hormone replacement.

BACKGROUND: We recently demonstrated that hypophysectomy profoundly inhibits metastatic behavior in the MGH-OGS murine osteosarcoma model and speculated that this effect is related at least in part to ablation of the growth hormone (GH)-insulin-like growth factor I (IGF-I) axis. PURPOSE: In this study, we determined whether the administration of GH to animals rendered GH and IGF-I deficient by hypophysectomy attenuates the inhibitory effects of hypophysectomy on metastatic behavior. METHODS: Metastatic behavior was assayed by counting visible metastases in lungs 3 weeks after tail vein injection of RIF-I fibrosarcoma cells to control mice (n = 29), hypophysectomized mice (n = 19), and hypophysectomized mice administered 0.05 microgram/g body weight recombinant human GH twice daily (n = 21). RESULTS: Twenty of 21 hypophysectomized mice receiving GH, eight of 19 hypophysectomized mice not receiving GH, and 26 of 29 controls had grossly visible pulmonary metastases 3 weeks after intravenous injection of 5 x 10(5) cells; mean numbers +/- SD of gross metastases were 38.4 +/- 11.3, 6.4 +/- 2.2, and 13.1 +/- 2.8 in the three groups, respectively. The presence (P < .005, chi-square test) and number (P = .0003, Mann-Whitney U test) of metastases were significantly reduced in hypophysectomized hosts compared with control hosts and were significantly higher in hypophysectomized, GH-replaced hosts compared with hypophysectomized hosts (P < .001, chi-square test; P = .011, Mann-Whitney U test), while the difference in presence and extent of metastases between control and hypophysectomized, GH-replaced hosts was not statistically significant. CONCLUSIONS: These data support the hypothesis that the status of the host with respect to GH and/or GH-dependent factors such as IGF-I influences the metastatic behavior of certain neoplasms. IMPLICATIONS: Our results raise the possibility that compounds that reduce GH output or interfere with GH action, such as somatostatin analogues, GH antagonists, IGF antagonists, and GH-releasing hormone antagonists, may suppress metastatic behavior of certain neoplasms.

Animals↗

PubMed1996

Effect of hypophysectomy, sex of host, and/or number of transplanted testes on Sertoli cell number and testicular size of syngeneic testicular grafts in Fischer rats.

One or more neonatal testicular grafts were transplanted for 60-65 days into young adult inbred Fischer rats to determine the effect of hypophysectomy, sex of host, and/or the number of transplanted testes on testicular size and Sertoli cell number. All host rats had been castrated or ovariectomized and some were hypophysectomized as well. At the end of the treatment, testes were fixed and embedded in Epon before histologic sections (0.5 micrometer or 20 micrometers) were evaluated by stereology. Testicular grafts placed in castrated adult male rats with intact pituitaries weighed more (p < 0.01) and had more (p < 0.01) Sertoli cells than those placed in hypophysectomized hosts. Testicular grafts that were recovered from hypophysectomized rats 34 days posttransplantation and placed in pituitary-intact males for 30 day had larger (p < 0.05) parenchymal weights and more Sertoli cells than did testes re-transplanted into hypophysectomized rats. However, this delayed period of Sertoli cell proliferation id not extend to 65 days of hypophysectomy. When two or four testes were transplanted into castrated males or ovariectomized female hosts for 65 days, there was no difference in the graft weights or Sertoli cell numbers between sexes. Four transplanted testes per rat produced more (p < 0.01) total testicular parenchyma and a greater (p < 0.01) number of Sertoli cells per testis than did two tests regardless of sex of the host. This model has shown that the period of Sertoli cell proliferation can be delayed by hypophysectomy, that Sertoli cell number can be influenced by endogenous hormones, and that a major component in regulation of testicular size is at the level of the testis in this model. Hence, this model should facilitate study of experimental endocrine manipulation control and potential experimental intervention to increase Sertoli cell number and testicular size.

Animals↗

PubMed1998

Hypophysectomy, high tumor necrosis factor levels, and hemoglobinemia in lethal endotoxemic shock.

Experimental models of lethal endotoxemia in rodents are widely used to delineate pathogenic mechanisms of inflammation, sepsis, and septic shock. One long-standing but poorly understood observation is that removal of the pituitary gland (hypophysectomy) renders experimental animals 1,000-fold more sensitive to the lethal sequelae of lipopolysaccharide (LPS). Previous explanations for this phenomenon focused on hypophysectomy-induced deficiencies of corticosteroids, because glucocorticoids effectively suppress the synthesis of tumor necrosis factor (TNF), which is a primary mediator of LPS lethality. We measured LPS-stimulated macrophage TNF release in the presence of serum from hypophysectomized rats to detect the appearance of an inducible 65 kDa protein that enhances TNF release. Surprisingly, the N-terminal amino acid sequence analysis of the isolated, purified protein revealed its identity as hemoglobin. Hypophysectomy significantly increases serum hemoglobin levels (control hemoglobin = 103+/-18 microg/mL versus hypophysectomized serum hemoglobin = 279+/-13 microg/mL; p < .05). Purified hemoglobin enhances TNF synthesis in LPS-stimulated macrophages by at least 1,000-fold, which is specifically inhibited by antihemoglobin antibodies. Thus, hemoglobin mediates increased TNF synthesis in endotoxemic, hypophysectomized rats. This mechanism of increased TNF release has potential implications for patients with hemoglobinemia following blood transfusion, surgery, injury, infection, or other conditions that can be associated with endotoxemia and sepsis.

Animals↗

PubMed1979

Pituitary hormones and the small bowel: effect of hypophysectomy on intestinal adaptation to small bowel resection in the rat.

The influence of pituitary hormones on intestinal adaptation to small bowel resection was studied by examining jejunal and ileal structure and function in control and in sham-operated rats, and in animals with 50% proximal or distal resection which were divided into three main groups: normally-fed, hypophysectomized. and pair-fed. The pituitary was removed 2 weeks before intestinal surgery and gut structure and function were studied 4 weeks later. The effectiveness of hypophysectomy was confirmed by histological examination of the aspirated pituitary, and by showing a significant subsequent reduction in weight of the testes and adrenals. Food intake and body weight fell significantly after removing the pituitary; intestinal surgery caused a transient further decrease in food intake. Measurements of intestinal villus height and crypt depth, indices of mucosal mass (mucosal wet weight, protein and DNA content/cm intestine), measurements of mucosal alpha-glucosidase activity, and in vivo galactose absorption/unit length of intestine all showed comparable results. In rats with an intact intestine, resection resulted in mucosal hyperplasia and increased segmental absorption. Following hypophysectomy, there was marked mucosal hypoplasia and hypofunction which seemed to be due largely to associated hypophagia since comparable changes were found in the pair-fed, sham-operated rats. However following pituitary removal, both distal jejunum and proximal ileum retained their capacity to regenerate though the magnitude of this adaptive change was much greater in the resected, pair-fed rats suggesting that hypophagia alone cannot explain the diminished adaptation to resection after hypophysectomy. By inference, pituitary hormones do influence the adaptive response to resection.

Adaptation, Physiological↗

PubMed1983

Hypophysectomy does not prevent increased cerebral dopamine turnover following sulpiride administration.

Hypophysectomy is claimed to prevent increased forebrain dopamine turnover produced by administration of sulpiride. We have measured the increase in dopamine metabolite concentrations caused by sulpiride following surgical removal of the pituitary. In saline-treated control animals and in hypophysectomized rats 1 week or 1 month following surgery, administration of sulpiride caused marked elevations of striatal, nucleus accumbens and tuberculum olfactorium, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations which were maximal 4-8 h following drug administration. The maximal increases in nucleus accumbens and tuberculum olfactorium were generally comparable in control and hypophysectomized animals, except for a greater increase in HVA levels in the nucleus accumbens 1 month following hypophysectomy. However, maximal increases in HVA and DOPAC in striatum were more pronounced in hypophysectomized rats 1 week or 1 month following surgery compared with control animals. At 30 min following sulpiride administration only inconsistent changes in dopamine turnover were observed in both control and hypophysectomized rats. Hypophysectomy does not prevent sulpiride from increasing forebrain dopamine turnover suggesting this is due to a direct interaction with cerebral dopamine receptors.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1978

Time course of mesenteric vasodilatation following hypophysectomy and the stopping of a vasopressin infusion.

Hypophysectomy caused an increase in superior mesenteric arterial conductance that reached a new plateau approximately 20 min after removal of the gland in four pentobarbital-anesthetized cats. Intravenous infusion of arginine vasopressin (0.74 +/- 0.21 mU min-1kg-1) caused conductance to decrease to approximately prehypophysectomy control values. Stopping the infusion resulted in an increase in conductance and the time course of this vasodilatation was virtually identical to that which occurred following hypophysectomy. The results are consistent with the interpretation that the effects of acute hypophysectomy on the mesenteric resistance vessels are due primarily to removal of the vasopressin system and the concomitant elimination of circulating vasopressin.

Animals↗