Experimental model of immune-mediated hearing loss using cross-species immunization

The presence of immune-mediated hearing loss was investigated in an animal model. Eight guinea pigs and four mice underwent immunizations with a preparation of chick or guinea pig cochlear tissue and Freund's adjuvant. Hearing thresholds were monitored by auditory brainstem response (ABR) testing over a 5-week period after immunization. The serum and temporal bones of test and control animals were then examined using an enzyme-linked immunosorbent assay (ELISA), immunocytochemical, and histological techniques. Hearing loss of 20 dB or greater occurred in eight animals. ELISA demonstrated antibodies to cochlear antigens in the sera of all test animals. Immunocytochemistry revealed immunostaining of hair cell stereocilia in the organ of Corti and saccule. Endolymphatic hydrops, and organ of Corti degeneration was observed in the temporal bones of three animals. This study provides evidence to suggest that cross-species immunization with cochlear antigens might produce a humoral response that can be associated with inner ear pathologic change and sensorineural hearing loss.

Cholinergic mechanisms of cutaneous active vasodilation during heat stress in cystic fibrosis

To test the hypothesis that cutaneous active vasodilation in heat stress is mediated by a redundant cholinergic cotransmitter system, we examined the effects of atropine on skin blood flow (SkBF) increases during heat stress in persons with (CF) and without cystic fibrosis (non-CF). Vasoactive intestinal peptide (VIP) has been implicated as a mediator of cutaneous vasodilation in heat stress. VIP-containing cutaneous neurons are sparse in CF, yet SkBF increases during heat stress are normal. In CF, augmented ACh release or muscarinic receptor sensitivity could compensate for decreased VIP; if so, active vasodilation would be attenuated by atropine in CF relative to non-CF. Atropine was administered into skin by iontophoresis in seven CF and seven matched non-CF subjects. SkBF was monitored by laser-Doppler flowmetry (LDF) at atropine treated and untreated sites. Blood pressure [mean arterial pressure (MAP)] was monitored (Finapres), and cutaneous vascular conductance was calculated (CVC = LDF/MAP). The protocol began with a normothermic period followed by a 3-min cold stress and 30-45 min of heat stress. Finally, LDF sites were warmed to 42 degrees C to effect maximal vasodilation. CVC was normalized to its site-specific maximum. During heat stress, CVC increased in both CF and non-CF (P < 0.01). CVC increases were attenuated by atropine in both groups (P < 0.01); however, the responses did not differ between groups (P = 0.99). We conclude that in CF there is not greater dependence on redundant cholinergic mechanisms for cutaneous active vasodilation than in non-CF.

Pulmonary fibrosis with small-airway disease: a model in nonhuman primates

Bleomycin was administered intrabronchially to four baboons in doses of 1 mg/kg for four consecutive weeks. At necropsy 6 months later, the lesions produced differed markedly from those resulting from parenteral administration of bleomycin and consisted of diffuse foci of inflammation and fibrosis of the lung parenchyma associated with small airway lesions. Airway lesions were found in respiratory bronchioles and consisted of bronchiolar wall inflammation, hyperplasia of smooth muscles, and epithelia bronchiolization of adjacent alveolated structures. Many bronchioles were obliterated by the fibrotic process. Biochemical measurements confirmed the histologic appearance of increased lung collagen in three of four animals. These findings indicate that obstruction of small airways by processes which cause lung fibrosis may be separable physiologically from processes which affect only the lung parenchyma.