Stapedectomy in the guinea pig.

Stapedectomy has traditionally been studied in the feline model. Ethical considerations and costs have made this model less feasible for ongoing research. The purpose of this study was to examine the guinea pig as a model for research on stapedectomy. Technical difficulties included limited exposure and small dimensions of the ossicles. The surgical technique with and without the use of a CO(2) laser and the relevant anatomy of the guinea pig middle ear are described.     

Diabetes mellitus.

Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. The chronic hyperglycemia of diabetes mellitus is associated with long-term damage, dysfunction, and failure of various organs, especially the eyes, kidneys, nerves, heart, and blood vessels. The management of this disease process is complicated. Good diabetic control depends on diligence in blood glucose monitoring, frequent adjustment of medications, adherence to a regular diet and exercise plan, and treatment of comorbid conditions such as hypertension and hyperlipidemia.     

Labyrinthine fenestration in the guinea pig.

OBJECTIVE: To evaluate the auditory effects of single, double, and triple semicircular canal fenestration procedures, with and without sealing the labyrinthine defect. BACKGROUND: Violation of the inner ear remains a feared complication in otologic surgery because it commonly leads to profound sensorineural hearing loss. It has been assumed that the natural history of labyrinthine injury in the guinea pig is similar to that in human beings; however, this assumption has not been rigorously studied. DESIGN: Prospective, randomized, and controlled animal study. SUBJECTS: Sixty pigmented guinea pigs. OUTCOME: Click-evoked electrocochleographic response, with same-ear prefenestration control. RESULTS: All of the fenestration groups had elevated auditory thresholds at 1 hour when compared with controls (P < 0.01); however, this difference lost statistical significance at 1 and 4 weeks. The degree of labyrinthine injury did not correlate with the degree of hearing loss or with the incidence of anacusis. Hearing remained stable during the study period. Sealing the fenestration had no significant audiologic effect (P > 0.40). CONCLUSIONS: The guinea pig model of labyrinthine fenestration may not be representative of the human condition.     

Complement-independent nephrotoxic nephritis in the guinea pig.

Immunologic mechanisms of proteinuria were investigated in guinea pigs (GP) injected with sheep antiserum (NTS) to GP glomerular basement membrane (GBM). Linear deposition of sheep gamma 1 and gamma 2 IgG led to a prompt but transient (36 hr) increase in albumin excretion from control values of 0.026 +/- 0.013 mg/hr to maximal values of 26+/-12.1 mg/rh at six hours without detectable histologic or electron microscopic changes except for decreased staining for glomerular polyanion and epithelial cell foot process fusion. GBM permeability to anionic ferritin was not increased during proteinuria. Anti-GBM antibody deposits did not fix GP C3 or C4 in vivo or in vitro. NTS-induced proteinuria was the same in guinea pigs that were normal, greater than 95% depleted of C3 through C9, genetically deficient in C4, and depleted of circulating polymorphonuclear leukocytes (PMN). Prior administration of antihistamines, steroids, azathioprine, colchicine, indomethacin, heparin, aprotinin (Trasylol), and niridazole also failed to reduced proteinuria. Initial proteinuria subsided by 36 hr, did not recur despite linear deposition of GP gemma 1 and gemma 2 after day seven, and antibody to GMB-bound sheep globlin. In the GP nephrotoxic nephritis model, anti-GBM antibody deposits apparently mediate increased permeability to albumin by a currently undefined mechanism which is independent of complement, PMN, and other know mediators of inflammation.     

Subanesthetic halothane is hepatotoxic in the guinea pig.

Subanesthetic concentrations of halothane were examined for their hepatotoxic potential in the guinea pig. Outbred male, Hartley guinea pigs (600-700 g) were exposed to either 1.0%, 0.25%, or 0.10% (vol/vol) halothane, 40% O2, for 4 h. Plasma isocitrate dehydrogenase (ICDH) activity was compared to plasma alanine aminotransferase (ALT) for sensitivity as an indicator of hepatic injury. As previously seen, exposure to the anesthetic concentration of 1.0% halothane produced limited to confluent centrilobular necrosis in 50% (4/8) of the guinea pigs. The subanesthetic concentrations of 0.25% and 0.1% halothane were also hepatotoxic. After exposure to 0.25%, confluent centrilobular necrosis developed in 2 of 8 animals, whereas 0.10% halothane produced limited centrilobular necrosis in 3 of 8. Plasma ICDH activity was a more sensitive indicator of halothane-induced hepatic injury than ALT. Mean plasma ALT activity increased significantly after 1.0% halothane exposure only. However, ICDH activity was significantly increased after exposure to all three concentrations of halothane. Comparison of peak plasma enzyme activities demonstrated significantly larger increases in ICDH than in ALT when centrilobular necrosis was present. Use of subanesthetic concentrations of halothane should help overcome the many transient effect that high concentrations of halothane have on whole liver and hepatocyte functions. By being able to isolate and titrate the bioactivation of halothane, the mechanisms through which halothane biotransformation produces acute hepatotoxicity should be more easily elucidated.     

Effect of ibuprofen upon hearing in the guinea pig.

The authors investigated the effect of varying doses of ibuprofen upon the hearing of guinea pigs monitored with brain stem-evoked response procedures. In daily dosages comparable on a weight basis to therapeutic levels in humans, ibuprofen was found not to have significant effects on response threshold or latency characteristics.     

Hyperbaric compression in the guinea pig with perilymph fistula.

OBJECTIVE: The study goal was to evaluate the effects of hyperbaric therapy on the auditory and vestibular function of guinea pigs compromised by perilymph fistula (PLF). METHODS: Twenty-four pigmented guinea pigs underwent induction of bilateral eustachian tube dysfunction before the creation of a unilateral PLF. Half of the animals were randomly assigned to receive immediate hyperbaric compression treatment of 4 "dives" each. Hearing was tested electrocochleographically, and signs of vestibulopathy were recorded before and after compression. RESULTS: After accounting for the effects of PLF, compression was not associated with significant hearing loss (P = 0.5411). Vestibulopathy was seen only in ears with PLF, and its incidence was similar for compression and noncompression groups. CONCLUSION: Hyperbaric compression does not compromise auditory or vestibular function in guinea pig ears with experimental PLF. SIGNIFICANCE: Our observations support the relative safety of recompression in patients with PLF.     

Gonadotrophin-like substance in the testis. Immunocytochemical localization in the guinea pig

A gonadotrophin-like material (GLM) was observed by immunocytochemical methods in prepuberal guinea pig testes, not only on Sertoli and interstitial cells, but also on spermatogonia and spermatocytes. The intracellular cytoplasmic localization of GLM is discussed in relation to the receptor internalization theory. Variations between young and adult animals allowed us to approach the physiological significance of testicular GLM.     

Changes in testis of guinea pig after vasectomy.

Thirty adult guinea pigs were bilaterally vasectomized and subsequently sacrificed at one, three, and six months after operation. Cell counts were performed on five seminiferous tubules from each animal to identify and quantitate changes in spermatogenesis. Forty-three per cent of the animals had alterations in spermatogenesis that were characterized by generalized hypospermatogenesis and presence of multinucleated spermatids. There was a high incidence (93 per cent) of sperm-agglutinating antibodies in the vasectomized group. Sperm antibodies were not detected in the normal and sham-operated animals. Mean testicular weights and seminiferous tubule diameters were significantly reduced in the hypospermatogenic animals. The intersitial tissue of the vasectomized and sham-operated animals was morphologically indistinguishable from that of unoperated animals.     

Diabetes mellitus with immune complex glomerulonephritis.

The present study describes 3 patients with the simultaneous occurrence of diabetic nephropathy and immune-complex mediated glomerulonephritis. Renal manifestation included proteinuria and hematuria which were preceded by or co-existent with an infectious process. Renal manifestation included proteinuria and hematuria which were preceded by or co-existent with an infectious process. Renal histology showed the characteristic change of diabetic nephropathy along with those of immune complex glomerulonephritis. Immunofluorescence studies showed a linear pattern with a superimposed granular pattern of IgG and C3 deposits. Renal function and urinary findings improved in the 2 patients who were followed up.     

Reaction to silicone implants in the guinea pig

Many papers have been published on the lack of reaction around silicone implants both in the experimental animal and the human. A study with human silicone implants with silicone gel interior shows loss of the silicone fluid from intact silicone sac. A solid silicone disc subjected to 5 pounds weight for one week loses silicone to the underlying paper. In the guinea pig, some capsules surrounding solid silicone implants, silicone sacs with saline, and silicone sac with silicone gel show vacuole or amorphous materials (silicone) with a thickening of the capsule and associated inflammatory reaction. These vacuoles or amorphous material resembles the silicone found in capsules around intact human silicone jell prosthesis. The presence of silicone with associated thickening of the capsule and inflammatory reaction may be one cause of firmness in the human after breast augmentation by silicone implants.     

Kit positive cells in the guinea pig bladder

PURPOSE: We describe the presence of interstitial cells of Cajal (ICC) throughout the wall of the guinea pig bladder. MATERIALS AND METHODS: Bladders obtained from male guinea pigs were prepared for immunohistochemical investigations using various primary antibodies, including the specific ICC marker c-kit (Gibco BRL, Grand Island, New York). Enzymatically dispersed cells with a branched morphology were identified as ICC using anti-c-kit. They were loaded with fluo-4acetoxymethyl (Molecular Probes, Eugene, Oregon) and studied using confocal laser scanning microscopy. RESULTS: Anti-c-kit labeling demonstrated that ICC were oriented in parallel with the smooth muscle bundles that run diagonally throughout the bladder. Double labeling with anti-smooth muscle myosin (Sigma Chemical Co., St. Louis, Missouri) revealed that ICC were located on the boundary of smooth muscle bundles. When anti-c-kit was used in combination with the general neuronal antibody protein gene product 9.5 (Ultraclone Ltd., Isle of Wight, United Kingdom) or anti-neuronal nitric oxide synthase, it was noted that there was a close association between nerves and ICC. Enzymatic dissociation of cells from tissue pieces yielded a heterogeneous population of cells containing typical spindle-shaped smooth muscle cells and branched cells resembling ICC from other preparations. The latter could be identified immunohistochemically as ICC using anti-c-kit, whereas the majority of spindle-shaped cells were not Kit positive. Branched cells responded to the application of carbachol by firing Ca2+ waves and they were often spontaneously active. CONCLUSIONS: ICC are located on the boundary of smooth muscle bundles in the guinea pig bladder. They fire Ca2+ waves in response to cholinergic stimulation and can be spontaneously active, suggesting that they could act as pacemakers or intermediaries in the transmission of nerve signals to smooth muscle cells.     

Droperidol prevents serotonin-induced bronchospasm in the guinea pig

The effects of droperidol on bronchoconstriction induced by serotonin (5-HT) were studied in mechanically ventilated, paralyzed guinea pigs that had been anesthetized with pentobarbital. Droperidol did not modify the resting bronchial tone but prevented the bronchoconstrictor effects of 5-HT in a dose-related manner. Pretreatment with propranolol, hexamethonium, or prazosin did not alter the protective effects of droperidol on 5-HT-induced bronchoconstriction. The bronchoconstrictor responses to histamine or acetylcholine were not affected by droperidol. These results suggest that the protective effects of droperidol on 5-HT-induced bronchoconstriction are mediated through 5-HT receptor blockade on bronchial smooth muscle.