A obstrução uretral é uma condição clínica comum em gatos, caracterizada por alterações metabólicas e do equilíbrio hidroeletrolítico e ácido-básico que são potencialmente fatais. Dentre as causas de obstrução uretral, a cistite idiopática é a mais frequentemente observada em diversos estudos. Outras causas incluem urolitíase, tampões uretrais e infecção do trato urinário. Em muitos casos, os gatos encontram-se em estado crítico e a morte pode ocorrer em decorrência de alterações metabólicas, como estado urêmico avançado e hipercalemia. As principais alterações eletrolíticas e do equilíbrio ácido-básico relatadas são hipercalemia, acidose metabólica, hiponatremia e hipocalcemia ionizada. Embora a obstrução uretral seja muito frequente na rotina clínica, estudos para caracterizar a população de gatos acometida ainda são escassos no Brasil. Características relacionadas ao manejo, dieta e perfil dos tutores podem influenciar na manifestação da doença. Os objetivos do presente estudo foram avaliar os parâmetros clínicos e as alterações hematológicas, bioquímicas, urinárias, eletrolíticas e ácido-básicas presentes em gatos com obstrução uretral e a associação entre estas variáveis. Além disso, objetivou-se conhecer as principais causas de obstrução uretral nos gatos atendidos no Hospital de Clínicas Veterinárias da Universidade Federal do Rio Grande do Sul. Para isso, foram incluídos no estudo 28 gatos com diagnóstico de obstrução uretral no período de dezembro de 2015 a dezembro de 2016. Foram obtidos dados referentes ao histórico, exame físico, coletados sangue e urina, além da realização de exames de imagem (radiografia e ultrassonografia abdominal). Em todos os gatos foram realizados hemograma, bioquímica sérica, análise de pH, gases e eletrólitos sanguíneos, urinálise e urocultura. Após, todos os pacientes foram tratados de acordo com um protocolo pré-estabelecido. A causa mais comum de obstrução uretral neste estudo foi a cistite idiopática, que ocorreu em mais de 60% dos casos, seguida de tampões uretrais e infecção do trato urinário. Nenhum caso de urolitíase foi diagnosticado, o que pode ser explicado por fatores como idade, ambiente e estilo de vida dos animais. A maioria dos gatos obstruídos apresentou múltiplos sinais sistêmicos, assim como alterações metabólicas, eletrolíticas e do equilíbrio ácido-básico, principalmente azotemia, hiperlactatemia, acidose metabólica, hipercalemia e hipocalcemia ionizada. Hipotermia, depressão do estado mental, bradicardia e desidratação foram os parâmetros clínicos que tiveram maior quantidade de associação com as alterações metabólicas e podem ser considerados bons preditores clínicos destas desordens. Por outro lado, o lactato não foi considerado um bom preditor de alterações clínicas e laboratoriais neste estudo. / Urethral obstruction is a common and potentially life-threatening condition, characterized by severe metabolic, electrolyte and acid-base disturbances. Among the causes of urethral obstruction, idiopathic cystitis is the most frequent in several studies. Other causes include urolithiasis, urethral plugs and urinary tract infection. In many cases, cats are critically ill and death may occur due to metabolic alterations, such as advanced uremic status and hyperkalemia. The main electrolyte and acid-base balance disorders reported are hyperkalemia, metabolic acidosis, hyponatremia and ionized hypocalcemia. Although urethral obstruction is a very common condition, there are few studies characterizing the population affected by the disease in Brazil. Characteristics related to management, diet and owner’s profile can influence the manifestation of the disease. The aim of the present study was to evaluate the association of clinical, haematological, biochemical, urinary, hydroelectrolyte and acid-base parameters in male cats with urethral obstruction. In addition, the objective was to determine the causes of urethral obstruction in male cats admitted to the Veterinary Teaching Hospital of Federal University of Rio Grande do Sul. Twenty-eight cats diagnosed with urethral obstruction were included in the study between December 2015 and December 2016. Data regarding medical history and physical examination were obtained. Blood and urine were collected, and imaging tests were performed (abdominal radiography and ultrasonography). Complete blood count, serum chemistry, blood pH, gas and electrolyte, urinalysis and urine culture were performed. All patients were treated accordingly to a previous established protocol. The most common cause of urethral obstruction in this study was idiopathic cystitis, which occurred in more than 60% of cases, followed by urethral plugs and urinary tract infection. No diagnosis of urolithiasis was achieved which could be explained by factors like age, environment and life style of cats. Most of obstructed cats presented with multiple systemic clinical signs, as well as, metabolic, electrolyte and acid-base alterations. The main disorders found were azotemia, hyperlactatemia, metabolic acidosis, hyperkalemia and ionized hypocalcemia. Hypothermia, depressed mental status, bradycardia and dehydration were the clinical parameters with the greatest amount of associations with the metabolic alterations and can be considered as good predictors of metabolic disorders. On the other hand, lactate was not considered a good predictor of clinical and laboratory abnormalities in this study.

Teleost fishes incorporate renal ammonia excretion as part of a greater acid-base regulatory system. However, the transport mechanisms employed by the renal epithelium to excrete ammonia are relatively unknown. I hypothesized that, under metabolic acidosis, increased renal ammonia excretion would be the product of tubular secretion and involve a Na+/NH4+ exchange metabolon mediated through Rhesus (Rh) glycoproteins. To induce metabolic acidosis, goldfish (Carassius auratus) were exposed to a low pH environment (pH 4.0; 48-h). There was a clear signal of metabolic acidosis: a reduction in both plasma [HCO3-] and blood pH with no influence on plasma PCO2. Goldfish demonstrated an elevation in total plasma [ammonia] with a reduction in PNH3 under acidosis. Metabolic acidosis induced higher rates of urinary excretion of acidic equivalents in the form of both NH4+ and titratable acidity-HCO3- (TA-HCO3-) excretion. Urinary Na+ excretion was not affected by acidosis and urine [Na+] did not correlate with urinary [ammonia]. Alanine aminotransferase activity in the kidney was higher in acidotic goldfish. Glomerular filtration rate and urine flow rate were not affected by acidosis. Increased renal NH4+ excretion was due to increased secretion, and not increased filtration, of ammonia. There was a corresponding elevation in Rhcg1b mRNA expression but no change in renal Na+ reabsorption. My data support a secretion-based mechanism of teleost renal ammonia transport. This system is Na+ independent and is likely mediated by Rh glycoproteins and H+ ATPase, involving a parallel H+/NH3 secretion mechanism. To investigate effects of metabolic acidosis on elasmobranch fish, Pacific spiny dogfish (Squalus acanthias suckleyi) were infused with an acidic saline (125 mM HCl/375 mM NaCl; 3 ml/kg/h; 24-h). The results are preliminary, with no marked effects of HCl infusion on plasma acid-base or N-status, but increased branchial NHE2 and lower renal NHE3 protein expressions. These data are summarized in an Appendix. / Thesis / Master of Science (MSc)