Sham-operated Guinea Pigs Research Articles

Histomorphometric changes in the ovaries of thymectomized guinea pigs

Hypothalamic-pituitary-gonadal axis function is necessary for maintaining proper female reproductive cycle. This study aimed to evaluate the ovarian histomorphometric and histoarchitectural changes in neonatal, prepubertal and pubertal thymectomized female guinea pigs. A total of 30 female guinea pigs, sham-operated (n-5) and thymectomized (n-5) were studied in each group. The diameter and number of ovarian follicles among the thymectomized and sham operated female guinea pigs during estrus phase of estrous cycle was compared. Gonadal and accessory reproductive organs weights and microscopic features were studied in the sham operated guinea pigs and thymectomized. There were statistically significant changes in the number and diameter of follicles in the ovary in neonatal thymectomized female guinea pigs, but no significant changes were observed in prepubertal and pubertal female guinea pigs. Neonatal thymectomized female guinea pigs showed significant changes in their weight as well as changes in the microscopic features including reduced thickness of myometrium of uterus and less mucosal folding in the fallopian tube compared to the sham-operated group. But prepubertal and pubertal thymectomy did not affect the weight and microscopic features of gonads and accessory reproductive organs. Depending on the time of thymectomy, these results indicate morphological changes in the ovaries after thymectomy in females.

Effect of thymectomy on the female reproductive cycle in prepubertal and pubertal female guinea pigs

The proper function of the hypothalamic-pituitary-ovarian axis is essential for maintaining proper female reproductive function. In female mammals, the hypothalamic-pituitary-ovarian axis regulates reproductive changes that take place in the estrus cycle and are necessary for successful reproduction. This study aimed to investigate the influence of thymus gland on the female reproductive function in different stages of life. This present study was conducted to investigate the effect of thymectomy on the estrus cycle in prepubertal (5th week) and pubertal (7th week) thymectomized guinea pigs. In this study, 24 female guinea pigs, six thymectomized and six sham-operated in each group were studied. Gonadotropin and 17β-estradiol levels were assessed at regular intervals (days 0, 3, 6, 9, 12 and 15) of the estrus cycle, and the length of the oestrous cycle in the thymectomized and sham-operated guinea pigs was determined. The results showed no significant difference in gonadotropin and 17β-estradiol were detected in thymectomized versus sham-operated guinea pigs at any intervals of the oestrous cycle. Thymectomy did not affect the length of the oestrous cycle of females. In conclusion, the present study results suggested that the presence of thymus during prepubertal and pubertal life was not necessary to regulate the oestrous cycle of female guinea pigs.

Effect of thymectomy on the female reproductive cycle in neonatal guinea pigs.

ObjectiveThe appropriate function of the hypothalamic-pituitary-gonadal axis is essential for maintaining proper reproductive function. In female mammals, the hypothalamic-pituitary-gonadal axis regulates reproductive changes that take place in the estrus cycle and are necessary for successful reproduction. This study was conducted to investigate the effect of thymectomy on the estrus cycle in neonatally thymectomized guinea pigs.MethodsIn this study, 12 female guinea pigs, six thymectomized and six sham-operated, were studied. The effects of neonatal thymectomy at 5–7 days of age on parameters of the reproductive axis were examined in female guinea pigs. Gonadotropin and 17β-estradiol levels were assessed at regular intervals (days 0, 3, 6, 9, 12, and 15) of the estrus cycle, and the time of vaginal opening in the thymectomized and shamoperated guinea pigs was determined.ResultsSignificant reductions in gonadotropins and 17β-estradiol levels during estrus cycle were found in neonatally thymectomized female guinea pigs compared to sham-operated guinea pigs.ConclusionThe results of this study underscore the importance of the thymus in the neonatal period for normal female reproductive function.

Functional changes in low- and high-threshold afferents in obstruction-induced bladder overactivity.

Neural mechanisms of lower urinary tract symptoms in obstruction-induced bladder overactivity remain unclear. We made the first single unit recordings from different types of spinal afferents to determine the effects of bladder outlet obstruction in guinea pigs. A model of gradual bladder outlet obstruction in male guinea pigs was used to produce overactive bladder. Conscious voiding was assessed in metabolic cages, and micturition was recorded in anesthetized guinea pigs in vivo. Single unit extracellular recordings were made ex vivo from spinal afferent nerves in flat sheet preparations of the bladder. Guinea pigs with partially obstructed bladders showed a significant increase in conscious voiding frequency compared with sham-operated guinea pigs. Also, nonvoiding contractions increased significantly in both frequency and amplitude. Although spontaneous firing of low-threshold bladder afferents was increased, their stretch-induced firing was reduced. The proportion of capsaicin-sensitive low-threshold afferents increased in obstructed bladders. Interestingly, spontaneous and stretch-induced firing were both significantly increased in high-threshold afferents after obstruction. In summary, sensory signaling increased in the obstructed bladder during the filling phase. This is largely mediated by low-threshold stretch-sensitive afferents that are activated by increased local nonvoiding contractions. Increased spontaneous firing by high-threshold afferents also contributes. Our findings revealed a complex effect of bladder outlet obstruction on different types of bladder afferents that needs consideration for potential therapeutic targeting of lower urinary tract symptoms in obstruction-induced bladder overactivity.

Ubiquitin hydrolase (protein gene product 9.5) in the obstructed bladder: evidence for tissue remodelling involving a subset of interstitial cells

To examine the expression of ubiquitin hydrolase (UH), an enzyme which is part of the ubiquitin-proteasome system involved in the regulation of cell growth and differentiation, to gain an insight into the cell types and processes underlying the tissue remodelling that occur after bladder neck damage. Three groups of male guinea pigs were used, comprising controls (not operated, four), sham (five) and obstructed (six). The bladder outlet was obstructed by implanting a silver ring around the urethra, which was left in situ for 2-4 weeks. Sham-operated guinea pigs had the same operative procedure but no ring was implanted. The bladders were removed and incubated in Krebs' solution at 36 degrees C, gassed with 95% O2 and 5% CO2, Tissues were then fixed in 4% depolymerized paraformaldehyde and processed for immunohistochemistry. We used antibodies raised against UH, cyclooxygenase type I and vimentin. Specific antibody binding was visualized using the appropriate secondary antibodies. Staining with an antibody to UH showed the presence of both sensory and motor nerves in control, sham and obstructed bladders. In the control bladders this was the predominant staining pattern. In the sham and obstructed bladders UH staining revealed additional positive cell types; cells associated with the outermost layers of the urothelium (the umbrella cells), in the lamina propria (the lamina propria interstitial cells (lp-ICs), on the surface of the muscle bundles (surface muscle, sm-ICs) and on the serosal surface (muscle coat, mc-ICs). All ICs stained with vimentin. The ICs within the muscle bundles (intramuscular, im-ICs) did not stain with UH. The number and density of the UH-positive cells was greater in the obstructed than in the sham bladders, suggesting a change in relation to the severity of damage to the bladder neck. The expression of UH implies the re-targeting of proteins marked for degradation in the proteasome. Increased expression of UH in the lp-ICs and sm-ICs shows that these cells are active in the early and late stages of the tissue remodelling resulting from obstruction. These results show a further subset of ICs that might be involved in the increased deposition of extracellular material and tissue remodelling.

Effect of Nitric Oxide/Cyclic Guanosine Mono-phosphate Pathway on Gallbladder Relaxant Response in Bile Duct-Ligated Guinea Pigs

Background/Aims: Common bile duct ligation (CBDL) in the guinea pig is a well-defined model of acalculous cholecystitis. Nitric oxide (NO) mediates smooth muscle relaxation by stimulating the activity of soluble guanylate cyclase. The aim of this study was to determine whether the NO/cyclic guanosine monophosphate pathway plays a role in gallbladder relaxant response after CBDL. Methods: Relaxant response of gallbladder muscle strips from CBDL and sham-operated guinea pigs was studied in vitro. Animals were treated with saline, aminoguanidine or an aminoguanidine + L-arginine combination in vivo. Concentration-response curves of papaverine, diethylamine/NO, YC-1, sildenafil and amrinone were obtained and relaxations in each group were calculated as the percent of the contractions induced by carbachol (10^–6 M). Results: There was a significant decrease in the gallbladder muscle relaxant responses to these substances in CBDL and aminoguanidine groups compared with sham surgical controls. The decreased relaxant response was reversed by aminoguanidine + L-arginine but not by aminoguanidine alone. Conclusion: Decreased relaxant responses might be due to the reduced guanylate cyclase enzyme activity, but further studies are required.

Aging and total stenosis triggers differential responses of carotid and basilar arteries to endothelin-1 and phenylephrine

Our aim was to investigate the effects of ageing on the vascular contractility of carotid and basilar arteries from guinea-pigs, in a model of total stenosis. Moreover, we attempted to identify whether total stenosis of the left common carotid (stenosed) in adult guinea-pigs, would affect the contractions of contralateral carotid (intact) and basilar arteries to different vasoconstrictors. With this purpose, the left carotid was occluded with a silk thread at a position close to its origin. Vascular reactivity experiments using standard muscle bath were performed 7, 15, 30, and 90 days after carotid occlusion. Reactivity of carotid and basilar arteries to endothelin-1, phenylephrine and KCl was reduced with ageing in naive guinea-pigs. The endothelin-1 and KCl-induced contractions were unaltered in arteries from SHAM-operated animals. Moreover, phenylephrine-induced contractions were reduced in both carotids from 7 days SHAM-operated guinea-pigs, when compared to naive group. Stenosis induced progressive reduction in the contraction induced by endothelin-1, phenylephrine and KCl in the stenosed carotid, when compared to their respective age-matched naive and SHAM groups. Interestingly, an increased contractile-response to vasoconstrictor agents in all the contralateral carotids was observed. Stenosis (30 and 90 days) also induced an increase in the contractions induced by endothelin-1 in the basilar artery. Conversely, phenylephrine and KCl-induced contractions were reduced in basilar arteries 7, 15, 30 and 90 days after stenosis. These results showed that stenosis in adult guinea-pigs induce alterations of vascular reactivity in arteries distant from the site of injury. Thus, in spite of the common use of contralateral carotid as control, it must be aware of the potential alteration induced by stenosis in the vascular motility of such vessels. Additionally, it was verified a relationship between the period of stenosis and the alterations in the vascular reactivity to these vasoconstrictors.

Effects of NO/L-Arginine Pathway on Gallbladder Contractility in Bile Duct Ligated Guinea Pigs

Common bile duct ligation (CBDL) produces gallbladder distension and acute inflammation similar to that seen in human acute acalculous cholecystitis. CBDL in the guinea pig affects smooth muscle contractility. The aim of this study was to determine whether the nitric oxide-L-arginine pathway plays a role in the inflammatory process and abnormal gallbladder contractility that occur after CBDL. Contractility of gallbladder muscle from CBDL and sham-operated guinea pigs was studied in vitro. Animals were treated with saline, aminoguanidine (AG), or an aminoguanidine + L-arginine combination (AG + L-Arg) in vivo. Potassium chloride, carbachol, and electric field stimulation (EFS) were used for contracting the gallbladder muscle strips or activating intrinsic nerves. Hematoxylin and eosin-stained slides of muscle strips were scored for inflammation. Contraction responses to carbachol and EFS were decreased significantly in CBDL guinea pigs compared with those in the sham-operated group. AG partly reversed the smooth muscle contractile response to carbachol and EFS, but did not reduce the inflammation score. Treatment with AG + L-arg did not reverse either the contraction response or the inflammation score. These findings suggest that AG and AG + L-Arg treatments have no beneficial effect on inflammation in guinea pigs after CBDL, although AG significantly reversed the effect on muscle contractility (P < 0.05). This improvement was independent of inflammation and may be due to a decreased level of NO and its diminished relaxant effect.

Quantitative assessment of articular cartilage and subchondral bone histology in the meniscectomized guinea pig model of osteoarthritis

Objective: A new image analysis system was employed to quantify the main histological parameters reflecting osteoarthritic features, at the cartilage and bone levels, in the meniscectomized guinea pig model of osteoarthritis (OA). Methods: Meniscectomized (MNX) and sham-operated (SH) guinea pigs were studied 1 and 3 months after partial meniscectomy at the medial side of the left knee ( n=10 to 12 animals/group). The left proximal tibias were included in methylmethacrylate. Sections were cut and stained with safranin O or Goldner trichrome. Parameters were quantified using special programs of a Biocom image analyser. The following parameters were evaluated at the medial side of the tibia: cartilage thickness (CT); fibrillation index (FI); proteoglycan content ratio based on safranin O staining intensities (PC); chondrocyte density (CD); bone volume (BV) and subchondral bone plate thickness (SBPT). The degree of user interaction varied from manually tracing objects to almost complete computer automation. Results: Meniscectomy resulted in significant variations of these reproducible histomorphometric parameters both after 1 month (FI: +522%, P<0.01) and 3 months (FI: +162%, P<0.001; PC: −36.7%, P<0.001; CD: −31.8%, P<0.001; SBPT: +8.7%, P<0.05) post-operation (results expressed as percentage variation of MNX vs SH). The linear correlation analysis including data from SH and/or MNX animals at the two grouped time points revealed significant r values, in particular between cartilage (CT) and subchondral bone parameters (SBPT) (r=−0.41, P<0.01). Conclusions: Contrary to scoring evaluation, this system allowed to show the time-dependent impact of the pathology with an early fibrillation of the medial tibial cartilage appearing as soon as 1 month post-surgery, and the close relationship between bone and cartilage parameters during the progression of OA.

The spleen modulates the febrile response of guinea pigs to LPS.

The febrile responses of splenectomized (Splex) or sham-operated (Sham) guinea pigs challenged intravenously or intraperitoneally with lipopolysaccharide (LPS) 7 and 30 days after surgery were evaluated. FITC-LPS uptake by Kupffer cells (KC) was additionally assessed 15, 30, and 60 min after injection. LPS at 0.05 microg/kg iv did not evoke fever in Sham animals but caused a 1.2 degrees C core temperature (T(c)) rise in the Splex animals. LPS at 2 microg/kg iv induced a 1.8 degrees C greater T(c) rise of the Splex animals than of their controls. LPS at 2 and 8 microg/kg ip 7 days postsurgery induced 1.4 and 1.8 degrees C higher fevers, respectively, in the Splex than Sham animals. LPS at 2 and 8 microg/kg ip 30 days postsurgery also increased the febrile responses of the asplenic animals by 1.6 and 1.8 degrees C, respectively. FITC-LPS at 7 days was detected in the controls within KC 15 min after its administration; the label density was reduced at 30 min and almost 0 at 60 min. In the Splex group, in contrast, the labeling was significantly denser and remained unchanged through all three time points; this effect was still present 30 days after surgery. Similar results were obtained at 60 min after FITC-LPS intraperitoneal injection. Gadolinium chloride pretreatment (-3 days) of the Splex group significantly reduced both their febrile responses to LPS (8 microg/kg ip) and their KC uptake of FITC-LPS 7 days postsurgery. Thus splenectomy increases the magnitude of the febrile response of guinea pigs and the uptake of systemically administered LPS.

Effect of angiotensin type I–receptor blockade on left ventricular remodeling in pressure overload hypertrophy

Background: The renin-angiotensin system is involved in cardiac remodeling. In contrast to the well-recognized salutary effects of angiotensin-converting enzyme inhibition, the value of angiotensin II type I (AT1)-receptor blockade on left ventricular (LV) hypertrophy and dysfunction is controversial. Methods and Results: Descending thoracic aorta–banded and sham-operated guinea pigs were given either losartan (30 mg · kg−1 · day−1 intraperitoneally) or vehicle for 8 weeks (n = 7 in each group). LV end-diastolic and end-systolic dimensions and wall thicknesses were measured echocardiographically, and LV fractional shortening, relative wall thickness, and LV mass normalized by body weight were calculated. Isolated heart function (Langendorff perfusion) was studied 8 weeks after surgery, and LV performance was assessed by maximum LV pressure and ±dP/dt normalized by LV mass. Eight weeks after banding guinea pigs developed concentric LV hypertrophy and had decreased maximum LV pressure and ±dP/dt normalized by LV mass; LV end-diastolic dimension and LV fractional shortening were unchanged. In band-operated guinea pigs treatment with losartan had no significant effects on any of these measurements. Conclusions: In guinea pigs with descending aortic banding, treatment with losartan for 8 weeks neither attenuates progression of pressure overload hypertrophy nor significantly improves impaired mass-normalized pressure-derived indices of LV contraction and relaxation.

Effect of Indomethacin on Gallbladder Inflammation and Contractility during Acute Cholecystitis

Objective. The aim of this study was to determine whether the prostaglandin synthase inhibitor indomethacin reverses the inflammation and abnormal gallbladder contractility that occur after common bile duct ligation (CBDL), a model of acute cholecystitis.Methods. Gallbladder muscle contractility was studied in vitro in normal, CBDL, and sham-operated guinea pigs. Animals were treated with saline or indomethacin in vivo. Acetylcholine (ACh) was used to directly contract the muscle and electric field stimulation (EFS) to activate intrinsic nerves. Hematoxylin and eosin-stained slides of muscle strips were scored for inflammation.Results. CBDL in saline-treated animals increased the inflammation score and decreased gallbladder muscle contractility to ACh and EFS. Indomethacin decreased the inflammation score and partly reversed the smooth muscle contractile response to ACh 6 and 24 h after CBDL, but not at 48 h. Indomethacin did not reverse the CBDL-induced decrease in nerve-evoked contractions.Conclusion. Gallbladder inflammation and contractile dysfunction after CBDL are partly reversed with indomethacin at 6 and 24 h, but not at 48 h. This suggests that, early in the course of CBDL, the inflammation and contractile dysfunction are, in part, prostaglandin-mediated.

Effect of Acalculous Cholecystitis on Gallbladder Neuromuscular Transmission and Contractility

Background. Impaired smooth muscle contractility is important in the pathophysiology of acalculous cholecystitis. Common bile duct ligation (CBDL) is a model of acalculous cholecystitis, producing acute inflammatory changes and decrease in gallbladder smooth muscle contractility. The aim of this study was to determine whether there is coexistent dysfunction of neural efferent motor pathways of the gallbladder after CBDL.Materials and methods. Gallbladder muscle contractility was studied in vitro in normal, CBDL, and sham-operated guinea pigs. Electric field stimulation (EFS; 2–16 Hz) was used to activate intrinsic nerves and exogenous acetylcholine (ACh) was used to directly stimulate the muscle. H&E-stained slides of muscle strips were scored for inflammatory changes.Results. After CBDL, there was a progressive increase in the inflammation score and decrease in gallbladder muscle contractility to ACh. There was also a progressive decline in EFS-induced contractility when expressed as absolute force or normalized to the maximal muscle contractile response to ACh. The nitric oxide synthase inhibitor l-NNA (10 μM) increased EFS-induced contractions by 50 ± 25% (P = 0.05) in CBDL animals but had no effect in sham surgical controls.Conclusions. CBDL with its acute gallbladder inflammation affects gallbladder contractility by two mechanisms: (1) decreased smooth muscle contractility, and (2) decreased neurally mediated contractions. The neurally mediated alterations result from dysfunction of cholinergic excitatory nerves and upregulation of nitric-oxide-mediated inhibition of smooth muscle contractility.

Evidence of early subchondral bone changes in the meniscectomized guinea pig. A densitometric study using dual-energy X-ray absorptiometry subregional analysis

Objective Subchondral bone changes are thought to be an important aetiological element in the pathogenesis of osteoarthritis (OA). To confirm this hypothesis in the meniscectomized (MNX) guinea pig model, bone densitometry was performed in the subchondral bone of the distal femur.Methods MNX and sham-operated (SH) guinea pigs were studied 1 and 3 months after partial meniscectomy at the medial side of the left knee. Bone mineral density was measured at the lateral (BMD-L) and medial (BMD-M) sides of the distal femur using dual-energy X-ray absorptiometry (DXA). BMD-M was then compared to the bone volume evaluated by histomorphometry at the medial epiphyseal part of the proximal tibia (BV-M).Results One month after operation, in MNX animals left femur BMD-M was significantly lower than in the contralateral femur (−9%, P< 0.01) and than in the left femur of SH (−11%, P< 0.01). By contrast, 3 months after meniscectomy BMD-M was higher in the femur than in the contralateral femur (+4%, P< 0.05); BV-M tended to be higher on the left than on the right side (+4%, P< 0.06), and was significantly correlated with BMD-M at the 2 grouped time points: r=0.74 (P< 0.001).Conclusions These data emphasize the usefulness of DXA as a simple tool to assess subchondral bone changes at the OA-affected side of the femur and reveal typical variations of bone metabolism in the initiation of OA pathology in the MNX guinea pig: early bone loss at the subchondral level followed by increased bone density.

The role of cAMP in the frequency-dependent changes in contraction of guinea-pig cardiomyocytes.

beta-Receptor desensitisation, low basal cAMP, and a negative force-frequency relationship are characteristic changes in human heart failure. Isolated cardiomyocytes from noradrenaline-treated guinea pigs also show these features. We tested the hypothesis that low basal cAMP underlies the loss of contractile response to increasing stimulation frequency in this model. Isolated cardiomyocytes were obtained from noradrenaline-treated (NA) and sham-operated (SHAM) guinea pigs. They were stimulated from 0.1-2 Hz and contraction amplitude was monitored with a video edge-detection system. NA cells had less positive amplitude-frequency responses (AFR) compared to SHAMs at 2 mM (P = 0.002, n = 17), or midrange Ca2+ concentrations (EC40-EC60) (P < 0.001, n = 13). When the cAMP agonist, 8-CPT-cAMP (CPT, 10 microM) or high Ca2+ (above EC75) was added to NA cells the AFR was normalised to that of SHAM myocytes (NA vs. SHAM P = ns). In control experiments the cAMP antagonists, Rp-cAMPS (Rpc) and Rp-8-CPT-cAMPS (Rp8, 100 microM), blocked the positive inotropic effects of CPT at 0.5 Hz (control pD2 = 4.36 +/- 0.06, Rp8 pD2 = 3.68 +/- 0.08, P < 0.0001), n = 6 paired). Rpc (100 microM) completely but reversibly blocked the effect of maximal isoprenaline in control experiments (P < 0.0001). Neither antagonist reduced the AFR compared to time-matched controls (P = ns, n = 6). Blockade of SERCA2a with thapsigargin resulted in a significant reduction in the AFR (ANOVA P < 0.0001). The results are consistent with sarcoplasmic reticulum (SR) function being a more important determinant of the amplitude-frequency relationship than tonic levels of cAMP under basal conditions. Reversal of AFR depression by CPT may result from stimulation of SR Ca2+ uptake.

Fever suppression by subdiaphragmatic vagotomy in guinea pigs depends on the route of pyrogen administration.

It has recently been shown that subdiaphragmatic vagotomy blocks some of the effects of inflammatory stimuli on brain-controlled functions. Therefore, vagal afferent fibers have been proposed to play a prominent role in the communication pathways between the immune system and the brain. In the present study, we investigated the effect of subdiaphragmatic vagotomy on fever induced by intraperitoneal or intramuscular injection of lipopolysaccharide (LPS) or muramyl dipeptide (MDP), which are both cytokine-inducing agents in guinea pigs. Intraperitoneal and intramuscular injections of LPS or MDP were tested in the same animal with an interval of 1 wk. In one experiment, intraperitoneal injections of LPS or MDP were performed at the beginning, followed by intramuscular injections 1 wk later. In another experiment, intramuscular injections of LPS or MDP were performed at the beginning, followed by intraperitoneal injections 1 wk later. The febrile response to intraperitoneal injection of LPS was almost completely abrogated in vagotomized animals compared with sham-operated controls (from 30-330 min after intraperitoneal injection of LPS). The suppression of LPS fever was quantitatively the same in both experiments. In contrast, the response to intramuscular injection of LPS was the same in vagotomized and sham-operated guinea pigs in each of the experiments. Fever induced by intraperitoneal injection of MDP was partly attenuated by subdiaphragmatic vagotomy (between 150 and 300 min after intraperitoneal injection of MDP) in both experiments. Again, the febrile response to intramuscular injections of MDP was not significantly altered by subdiaphragmatic vagotomy. In conclusion, the suppressive effect of subdiaphragmatic vagotomy on fever induced by peripheral immune stimuli depends on the route of pyrogen administration. Because the febrile response to intraperitoneal injection of bacterial pyrogens is strongly diminished in vagotomized guinea pigs, it is suggested that vagal afferent fibers play a crucial role in the transduction of immune signals from the abdominal cavity to the brain.

Blockade of lipopolysaccharide-induced fever by subdiaphragmatic vagotomy in guinea pigs

It is generally believed that fever is mediated by certain cytokines produced by immune cells activated by exogenous pyrogens, e.g., lipopolysaccharides (LPS), released into the circulation and transported to the brain. There, the cytokines are thought to stimulate prostaglandin (PG) E 2 production within the organum vasculosum laminae terminalis region. PGE, then may act as a febrigenic mediator locally or in the surrounding preoptic area (POA). However, whereas the increases in preoptic PGE 2 and body (core) temperature (T c) following the intravenous (i.0 administration of LPS correlate temporally, cytokine levels in blood lag both these increases. From recent data in the literature, we have conjectured that a possible, alternative communication pathway between the i.v. LPS-activated immune system and brain PGE 2 may be provided by the vagi. To test this possibility, we measured the levels of PGE 2 in the extracellular fluid of the POA (collected by microdialysis) of conscious, subdiaphragmatically vagotomized or sham-operated guinea pigs following LPS administration (2 μg/kg; i.v.); controls received pyrogen-free saline (PFS). The effluents from the microdialysis probes were collected over 30-min periods throughout the experiments and the samples analyzed by radioimmunoassay; (T c) was monitored continuously using thermocouples inserted 5 cm into the colon. LPS induced a biphasic fall in T c and failed to increase preoptic PGE 2 levels in the vagotomized guinea pigs ( n = 10), whereas in their sham-operated controls ( n = 10) it induced increases in both preoptic PGE 2 and (T c) within 15 min after its injection; PFS ( n = 13) had no effect on either variable. We postulate that peripheral immune cell-derived signals may be transmitted via the vagi to the medulla. From other data, we suggest further that they may be conveyed from here via the ventral noradrenergic bundle to the POA region, where the released norepinephrine induces the local synthesis of PGE 2 and, hence, fever onset.

The N-methyl-D-aspartate-mediated inhibitory control of gonadotropin-releasing hormone release in the hypothalamus of the adult male guinea pig is expressed through opioidergic systems.

Previously, we reported on a dual role of N-methyl-D-aspartate (NMDA) receptor-mediated neurotransmission in the control of GnRH secretion from the medial basal hypothalamus (MBH) of the adult male guinea pig, with a predominantly inhibitory action in the intact animal, which is reversed to a facilitatory role by orchidectomy. In the present study we examined the hypothesis that endogenous opioids are involved in the NMDA receptor-mediated inhibition of GnRH release. A static incubation system was used to test the effects of excitatory amino acid agonists and an excitatory amino acid antagonist, alone or in the presence of either the opiate agonist morphine or the mu-receptor antagonist naloxone, on in vitro GnRH release from the isolated MBH of intact, orchidectomized, or sham-operated guinea pigs. GnRH output from the MBH of intact guinea pigs was markedly suppressed in the presence of the NMDA-specific receptor agonist, N-methyl-D,L-aspartic acid (NMA; 50 mM), whereas NMDA-specific receptor blockade with D,L-amino-5-phosphonovaleric acid (AP-5; 1 mM) resulted in a pronounced facilitation of GnRH release, as did exposure to the non-NMDA-specific receptor agonist, kainic acid (50 mM). Opioidergic blockade with naloxone (1 mM) caused a reversal of the responses to NMA and AP-5, with exposure to these compounds this time resulting in clear facilitation and inhibition, respectively. The stimulatory action of kainic acid, on the other hand, remained unaffected by the presence of naloxone. Morphine inhibited basal GnRH output and also annulled the stimulatory effect of AP-5 on GnRH secretion. The results obtained from MBHs of sham-operated guinea pigs were identical to those seen for the intact animals, with naloxone effectively increasing baseline GnRH release and reversing the inhibitory effect of NMA and stimulatory action of AP-5 on GnRH secretion to a facilitation and inhibition, respectively. On the other hand, NMA caused a marked stimulation, whereas AP-5 produced a significant inhibition of GnRH release from the MBHs of orchidectomized guinea pigs; neither of these effects was altered by the presence of naloxone, which, moreover, had only a marginal effect on basal GnRH output in this group of animals. In conclusion, our present data provide evidence to support the view that the primary inhibitory action of NMDA receptor-mediated neurotransmission on GnRH release in the MBH of the intact male guinea pig is the result of activation of opioidergic systems and that a marked reduction of opioid tone after orchidectomy brings a facilitatory NMDA receptor-mediated system to the fore. On the other hand, non-NMDA-specific kainate receptor-mediated facilitation of GnRH, previously shown to be unaffected by gonadal status, appears to be also independent from opioidergic modulation.

Catecholamine and beta-adrenoceptor influences on airway reactivity to antigen in guinea pigs.

The aim of the present study was to analyze the increased airway reactivity to antigen induced by beta-adrenoceptor blockade, adrenalectomy or medullectomy and to assess the contribution of circulating catecholamines to the increased reactivity. In anesthetized guinea pigs sensitized to ovalbumin (OA), administration of OA produced a dose-related bronchoconstriction characterized by threshold increases in airway insufflation pressure at 0.1 mg/kg i.v. and a near-maximal increase by 0.3 mg/kg i.v. Pretreatment with R(+) propranolol (0.5 mg/kg i.v.) 5 min prior to antigen did not significantly alter airway responses to antigen when compared to vehicle-treated animals. However, pretreatment with 0.5 mg/kg i.v. S(-) propranolol, racemic propranolol or nadolol markedly enhanced (10- to 15-fold) the airway response to the low-dose antigen. In addition, in guinea pigs which had been adrenalectomized, the reactivity to low-dose antigen was enhanced to a similar extent as that of beta-antagonist-treated animals when compared to sham-operated animals. Baseline plasma concentrations of epinephrine were significantly higher in sham-operate guinea pigs (1,494 +/- 223 ng/ml) when compared to adrenalectomized animals (412 +/- 44 ng/ml). Upon antigen exposure, epinephrine levels rose 5-fold (6,859 +/- 1,308 ng/ml) from baseline in sham-operated guinea pigs and were not significantly changed in adrenalectomized animals (848 +/- 208 ng/ml). Specific airway conductance measurements in conscious guinea pigs revealed that animals which had been medullectomized 2 weeks previously responded to lower provocative concentrations of aerosol OA (0.05-0.5%) than corresponding sham-operated animals. Airway reactivity to inhaled acetylcholine (0.1-1%) was similar in medullectomized and sham guinea pigs. Plasma concentrations of epinephrine were significantly lower in medullectomized guinea pigs (327 +/- 88 ng/ml) when compared to sham-operated animals (832 +/- 162 ng/ml). The results of the present study indicate that beta-adrenoceptor antagonism or changes in circulating epinephrine levels markedly alter the response to antigen in sensitized guinea pigs.

Ureteral obstruction in the neonatal guinea pig: Interaction of sympathetic nerves and angiotensin

The contribution of sympathetic nerves to the hemodynamic effects of unilateral ureteral obstruction (UUO) was investigated in the neonatal guinea pig. The left ureter was partially constricted (or sham-operated) at birth, and sympathetic innervation was inhibited by guanethidine and compared with saline vehicle-treated animals. At 15-20 days of age, blood pressure, cardiac output, total vascular resistance (TVR), renal blood flow, and renal vascular resistance (RVR) were determined before and after infusion of enalapril. UUO reduced cardiac output, increased TVR, and increased RVR of the ipsilateral kidney, whereas guanethidine treatment had no additional effects. Enalapril decreased RVR only in obstructed kidneys and not in intact opposite kidneys of animals with UUO. This was not affected by guanethidine administration. In contrast, enalapril decreased RVR only in guanethidine-treated (but not saline-treated) sham-operated guinea pigs. Therefore, UUO increases angiotensin-dependent vascular tone of the ipsilateral kidney independent of renal innervation. However, UUO decreases angiotensin-mediated vascular tone of the contralateral kidney, an effect unmasked by sympathectomy.