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Abstract.: We consider graphs whose vertices may be in one of two different states: either on or off . We wish to maintain dynamically such graphs under an intermixed sequence of updates and queries. An update may reverse the status of a vertex, by switching it either on or off , and may insert a new edge or delete an existing edge. A query tests whether any two given vertices are connected in the subgraph induced by the vertices that are on . We give efficient algorithms that maintain information about connectivity on planar graphs in O( log3 n) amortized time per query, insert, delete, switch-on, and switch-off operation over sequences of at least Ω(n) operations, where n is the number of vertices of the graph.

We investigated the outcome of reconstructive surgery of the urethra through guides composed of a novel biodegradable and highly biocompatible polymer, Hyaff-11. A tract of about 1.5 cm of the rabbit pendulous urethra was totally resected and replaced by a Hyaff-11 tubular graft. Eleven animals were analysed at each of the time points ranging from 7 days to 4 weeks following surgery. Histological and radiological evaluation showed a satisfactory remodelling of the neo-urethra around the implant. The regenerated connective tissue connected both urethral stumps within the first 7 days. On postoperative week 3, the Hyaff-11 guide had disappeared. At the 4-week time point the retrograde urethrogram showed a good distensibility of the neourethra. The regenerated stroma consisted of fibroblastic cells, and collagenous and elastic fibres. The neo-epithelium was pluristratified and exhibited cells of the cuboidal type.

Abstract: We designed long-term in vivo experiments to study rabbit urethral regeneration and remodelling over a hyaluronan biodegradable prosthesis. Seven months after the resection of a 1.5-cm-long tract of the urethra and its substitution with the prosthesis, radiological analysis showed the disappearance of the implant and the re-establishment of urethral continuity along the transmural defect. The regenerated tissue remodelled around the implant and exhibited good distensibility under pressure. Histological evaluation showed that the neo-urethra was lined with transitional epithelium and the stroma contained abundant elastic fibres. An examination of the pattern of the major cytoskeletal and cytocontractile proteins of smooth muscle cells and fibroblasts was able to distinguish fibroblasts from smooth muscle cells and myofibroblasts in the neo-urethra. These experiments provide evidence for the potential, successful use of biocompatible/bioresorbable devices for reconstructive surgery of the urethra.

Abstract.: Given a graph G with m edges and n nodes, a spanning tree T of G , and an edge e that is being deleted from or inserted into G , we give efficient O(n) algorithms to compute a possible swap for e that minimizes the diameter of the new spanning tree. This problem arises in high-speed networks, particularly in optical networks.

Experiments were performed to get further insights into the erectogenic mechanism of prostaglandin Et (PGEI), which was compared to that of papaverine (PAP). PGEI and PAP were effective in abolishing the contraction induced by N-ethylmaleimide (NEM), an adenylate cyclase blocker. However, preincubation with PGEI but not with PAP markedly attenuated the amplitude of adrenergic nerve mediated contraction following prolonged electrical field stimulation. Preincubation with PGEI was ineffective in counteracting the increase in tension due to exogenous norepinephrine. These data together with previous studies corroborate the hypothesis that in the presence of PGEI a dual erectogenic mechanism takes place in modulating the cyclic-adenosine-monophosphate metabolism of the cavernous smooth muscle cell as well as the release of norepinephrine from the sympathetic terminal.

In the present study we investigated the in vitro relaxant response of erectile tissue obtained from rabbits of different ages (3, 7 and 24 months) in order to detect the progression with age of cavernosal activity in response to substances acting via endothelium-dependent or-independent mechanisms. Noradrenaline induced a concentration-dependent contraction (0.1 µM–3 mM), with an increase in the contractility in the 24-month-old group. Acetylcholine produced a concentration-dependent relaxant effect in the three age groups, with a reduction of the maximal relaxant effect in older animals. ATP (10 µM–1 mM) and adenosine (10 µM–1 mM) induced a concentration-dependent relaxant effect that was higher in the older group. The presence of the NO-synthase inhibitor N?-nitro-L-arginine methyl ester (L-NAME) (0.1 mM) or of the P2-purinoceptor antagonist suramin did not affect ATP relaxation. Relaxation induced by sodium nitrite and nifedipine was reduced in older animals. In conclusion, aging selectively alters the in vitro responsiveness of rabbit erectile tissue. Purinergic system remains more active despite a decrease in the maximal endothelial cholinergic activity and the direct smooth muscle relaxant component.

Transplanted patients frequently present erectile impotence. In order to test any interference by cyclosporine A (CsA), which is commonly used in the post-transplantation management, we investigated the in vitro contractile and relaxant responses of corpus cavernosum and aorta from rabbits chronically treated with CsA. Male New Zealand White rabbits 6 months of age were treated with CsA (25 mg/kg per day s.c.) or solvent (corn oil) for 3 weeks. Descending thoracic aorta and erectile tissue were studied in vitro at the end of treatment. Isometric tension was recorded. In thoracic aorta, noradrenaline (0.1–30 mM) induced a concentration-dependent contraction with no difference betweer the two groups. Acetylcholine (30 mM–3 mM) produced relaxation (52±4% at 1 mM) that was significantly reduced in comparison to controls (67±4%, P<0.05). ATP (3–10 mM) relaxation was not significantly different (maximal 78±10% and 62±12% in CsA-treated and controls). The relaxation produced by sodium nitrite was reduced in CsA-treated rabbits (at 10 mM and 0.1 mM concentrations). In erectile tissue, no significant variation in the response of isolated erectile tissue to the above drugs was observed between CsA-treated and control animals. These data indicate that chronic treatment with CsA in rabbits, despite alteration of the in vitro response of thoracic aorta, does not directly influence the function of penile tissue with relaxants.

Abstract: We studied rabbit isolated erectile tissue responses to changes in preload and to active tension development with norepinephrine. The effects of antagonists of endothelin-1, prostaglandins E2 and F2αand of nitric oxide were also tested on normal and de-endothelialized preparations. Tissue distension was found to elicit spontaneous rhythmic contractions. Increase in preload diminished the latency of the spontaneous activity and augmented the developed force. Active tension development and the inhibitor of the Na+,K+ pump, ouabain, opposed the spontaneous activity. A marked reduction in the resting tension with abolition of the spontaneous activity was observed on normal, but not on de-endothelialized tissues, following the addition of the specific prostaglandin E2 and F2α receptor antagonist, SC-19220. At 3 × 10−4 M, the highest concentration used, the endothelin-A receptor antagonist BQ-123 failed to change the pattern of the spontaneous activity and the resting tension of normal tissues. The nitric oxide synthesis inhibitor, l-NAME, did not produce reliable effects. These findings point to a causal relation between cavernosal tissue distension and phasic and tonic contractions. Phasic contractions appear to be elicited by smooth muscle cells through the enzyme Na+,K+-ATPase. Increase in the resting tone could be mediated, at least in part, by the endothelium, through the release of prostaglandins E2 and/or F2αbut not of endothelins. We discuss the hypothesis that, in cavernosal tissue, mechanotransduction of distension to contractile responses is an important determinant of detumescence.

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