GLUT-4 Deficiency and severe peripheral resistance to insulin in the teleost fish tilapia.

Teleost fish, in general, are glucose intolerant; this trait has been attributed to piscine islets secreting insulin primary in response to amino acid secretogogues rather than glucose. However, pancreatic islet from the teleost fish tilapia, when transplanted into diabetic nude mice, were glucose responsive even though tilapia were severely glucose intolerant. This suggested a strong peripheral resistance to the glucostatic effects of insulin. Using Western blotting with polyclonal antibodies as well as Northern analysis for mRNA, tilapia tissues were found to be devoid of GLUT-4, the insulin-sensitive glucose transporter responsible for the hypoglycemic effect of insulin in mammals. The absence of GLUT-4 in peripheral tissues may explain why tilapia, and possibly other teleost fish, are severely glucose intolerant. This suggests that tilapia islets have evolved along mammalian lines to be glucose sensitive while tilapia peripheral tissue have diverged widely. Using the same methods, tilapia were found to have a very limited tissue distribution of the insulin-independent glucose transporter, GLUT-1, which is responsible for basal glucose transport in mammalian cells. It is suggested that tilapia provide a naturally occurring GLUT-4 knockout model.

Long-term function of fish islet xenografts in mice by alginate encapsulation.

BACKGROUND: Large, anatomically discrete pancreatic islets, Brockmann bodies (BBs), exist in certain teleost fish. When transplanted under the renal capsules of streptozotocin-diabetic athymic nude mice, BB grafts produce uniform normoglycemia for 50 days and mammalian-like glucose tolerance profiles; however, these very discordant islets reject in 7-8 days when transplanted into euthymic BALB/c mice. METHODS: In the present study, BBs were mass harvested, minced into <1-mm tissue fragments, and encapsulated in alginate-based macrospheres (5 mm diameter) or noodles (0.5x3 cm). Nonencapsulated and encapsulated BB fragments were transplanted intraperitoneally into streptozotocin-diabetic (nonfasting blood glucose >400 mg/dl) nu/nu and BALB/c mice. Glucose levels were monitored at least 3 times a week. RESULTS: Encapsulated BB grafts uniformly survived >50 days (10/10) or >100 days (3/3) in nu/nu recipients. The mean graft survival time was 27+/-13 days in BALB/c recipients (n=7). Daily intraperitoneal administration of 2.5 mg/kg 15-deoxyspergualin, in combination with encapsulation, resulted in uniform long-term BB graft function in BALB/c recipients (n=5). Similarly, long-term function was achieved in four of six BALB/c recipients with daily intraperitoneal administration of 10 mg/kg cyclosporine (two grafts failed after 39 and 45 days). Nonencapsulated BB grafts transplanted intraperitoneally into BALB/c or nu/nu recipients functioned for <7 days; immunosuppression alone did not permit graft survival in BALB/c recipients. In all cases of graft survival of >50 days, grafts were surgically removed from the peritoneal cavity, and blood sugar levels returned to a diabetic state within a few days. Historical sections of grafts, stained with hematoxylin and eosin and immunoperoxidase for insulin, showed viable, well-granulated BB tissue. CONCLUSIONS: This study demonstrates that tilapia BBs are suitable for encapsulation and that encapsulated BBs can be made to function long term in diabetic mice.

Management of impalpable testes: indications for abdominal exploration.

Various approaches to the management of the impalpable testis in cases of cryptorchidism have been advocated. The authors' experience over the past 13 years was reviewed to try to determine an optimal approach. Of 1,305 patients with undescended testicles seen between February 1982 and December 1995, 157 boys (12.03%) had impalpable testes with 17 having bilateral impalpable testes for a total of 174 impalpable testes. A hernia sac was present in 155 impalpable testes with a testicle present in all cases. No hernia sac was found in 19 impalpable testes, five of which had no testicle present. This was confirmed by either open exploration or laparoscopy. One hundred forty-eight boys underwent groin exploration as initial treatment, 13 of these had bilateral impalpable testes. In addition to the five absent testicles with no hernia sac, one patient with a hernia sac and no testicle evident benefited from subsequent laparoscopy to identify an intraabdominal testicle. All other patients underwent routine orchidopexy or orchidectomy (one case with grossly malformed testicle). Nine boys underwent laparoscopy as initial treatment, four of these had bilateral impalpable testes. Two abnormal testicles were found and removed. Groin exploration and subsequent orchidopexy was definitive treatment in all other cases. The association of a hernia sac with an impalpable undescended testicle is very significant (P < .00001 Fisher's Exact test). The absence of a sac therefore may reflect an alternate diagnosis. When no sac is found with a testicle in the groin, this may represent an ectopic testicle. When no sac is found with no testicle, this may represent a vanishing testicle. From this experience the authors conclude that groin exploration should be the initial approach to impalpable testes. The presence of a hernia sac with an absent testicle demands further exploration; the absence of a hernia sac with an absent testicle suggests a vanishing testicle and may need no further exploration.

Functional comparison of mouse, rat, and fish islet grafts transplanted into diabetic nude mice.

Equal volumes of teleost fish (tilapia), Lewis rat, or CD-1 mouse islets were transplanted under the kidney capsules of streptozotocin-diabetic athymic nude mice. Nonfasting blood glucose levels were monitored in recipient mice over a period of 30 days. Mean nonfasting blood glucose levels in recipients of tilapia (n = 7), rat (n = 8), and murine (n = 8) islets were 78.8, 77.0, and 115 mg/dl, respectively. Mean blood glucose levels were significantly higher in recipients of murine islets than in recipients of fish and rat islets. After Day 30, intraperitoneal glucose tolerance tests were performed on recipient mice. Mean fasted blood glucose levels in mouse, rat, and fish islet recipients were 113.3, 89.8, and 72.7 mg/dl, respectively. All three groups of recipient mice had similar glucose tolerance profiles with mean glucose disappearance rates (K values) between 4.3 and 5.7. Tilapia islet grafts resulted in a significantly lower baseline for blood glucose values than either rat or mouse islet grafts.