As rod photoreceptors are responsible for night vision, we administered isotretinoin to rats to learn whether night blindness resulted from rod cell death or from rod functional impairment. High-dose isotretinoin was given daily for 2 months and produced systemic toxicity, but this caused no histological loss of rod photoreceptors, and rod-driven electroretinogram amplitudes were normal after prolonged dark adaptation. Additional studies showed, however, that even a single dose of isotretinoin slowed the recovery of rod signaling after exposure to an intense bleaching light, and that rhodopsin regeneration was markedly slowed. When only a single dose was given, rod function recovered to normal within several days. Rods and cones both showed slow recovery from bleach after isotretinoin in rats and in mice. HPLC analysis of ocular retinoids after isotretinoin and an intense bleach showed decreased levels of rhodopsin chromophore, 11-cis retinal, and the accumulation of the biosynthetic intermediates, 11-cis and all-trans retinyl esters. Isotretinoin was also found to protect rat photoreceptors from light-induced damage, suggesting that strategies of altering retinoid cycling may have therapeutic implications for some forms of retinal and macular degeneration.vitamin A ͉ rhodopsin ͉ rat ͉ electroretinogram ͉ rod photoreceptor V isual response in vertebrate rod photoreceptors begins when light isomerizes the rhodopsin chromophore 11-cis retinal to all-trans retinal. The bleached photopigment activates the signal transduction cascade within the rod, leading to membrane hyperpolarization and thereby to retinal visual signaling. Part of the recovery mechanism from bleach requires reconversion of the chromophore to 11-cis retinal by enzymatic reactions (the vitamin A cycle) that occur within the adjacent retinal pigment epithelium (RPE) (1). Disruption of the vitamin A cycle retards restoration of night vision sensitivity. Human dietary vitamin A deficiency can cause night blindness (2), as does dietary substitution of retinoic acid in rats (3). Alternatively, night blindness can result from death and loss of rod photoreceptors in retinal degeneration (4), including some forms involving mutations in genes necessary for retinoid processing in the RPE (5). Some isotretinoin patients report impaired visual sensitivity at night and daytime glare sensitivity, suggesting photoreceptor compromise or loss (6). We have investigated the mechanism of isotretinoin-induced night blindness by evaluating ERGs, rates of rhodopsin regeneration, and retinoid processing in rats. We also evaluated the possible therapeutic benefit of isotretinoin in the rat light-damage model of retinal degeneration. Materials and MethodsAnimals. Protocols were approved by the University of Michigan's Committee on the Use and Care of Animals. SpragueDawley male 7-wk-old albino rats (Charles River Breeding Laboratories) were housed in 12:12 h light͞dark cycle of 5 lux fluorescent white light. Rats were fed high-fat breeding chow (Formulab; PMI Feeds, St. Lou...

No abstract

A specific peptide inhibitor of the cyclic AMP (cAMP)-dependent protein kinase (PKI-peptide) is a very effective inhibitor of the cAMP-dependent activation of motility of Ciona spermatozoa, when PKI-peptide is present at the beginning of incubation of demembranated spermatozoa with cAMP and ATP. Under conditions where approximately 120 sec is required for full activation of motility, the window of sensitivity to the PKI-peptide lasts for only 25-30 sec. Examination of sperm pellet proteins labeled with 32P ATP during activation reveals a major 25 kDa phosphoprotein and 2 minor phosphoproteins whose phosphorylation is highly sensitive to to inhibition by the PKI-peptide and essentially complete during this early phase. These sperm proteins appear to be immediate substrates for cAMP-dependent protein kinase, and phosphorylation of one or more of these appears to be requires, but not sufficient, for activation of motility. The phosphorylation of other proteins is reduced or eliminated when PKI-peptide is present at the beginning of incubation, but is unaffected by later addition of PKI-peptide. Some of these substrates appear to be likely candidates for axonemal proteins that must be phosphorylated during the later stages of incubation in order to complete the activation process. This selection is based upon a high degree of inhibition by inclusion of PKI-peptide or other inhibitors at the start of the incubation process, on near-completion of their phosphorylation by the end of the 2 min incubation period required for the activation of motility, and evidence that these proteins are phosphorylated during in vivo activation of motility. Although these observations suggest the presence of a second kinase activity that is upregulated by the initial activation of the cAMP-dependent protein kinase, assays using exogenous substrates have not yet been able to identify such a kinase activity.

ABSTRACT:We studied the effects of atrazine, isoproturon, metribuzin and sulfosulfuron on plant vigour, nodulation, chlorophyll content, seed yield and protein content in seeds, in greengram inoculated with Bradyrhizobium sp. (vigna). The pre-emergence application of the four herbicides at 400 µg kg -1 of soil adversely affected the measured parameters. The average maximum increase of 10 % in seed yield occurred at 200 µg kg -1 of sulfosulfuron, while atrazine at 200 and 400 µg kg -1 of soil decreased the seed yield by 25 % and 40%, respectively. The average maximum chlorophyll content of 1.2 mg g -1 was obtained at 200 µg kg -1 of sulfosulfuron which declined consistently for all herbicides and increasing dose rates. Sulfosulfuron at 200 µg kg -1 increased the number of nodules found per plant by 7 % at 45 days after seeding the greengram. In contrast, the tested dose rates of atrazine, isoproturon and metribuzin significantly reduced the nodulation (nodule number and dry mass). The average maximum grain protein of 182 mg g -1 was obtained for sulfosulfuron at 400 µg kg -1 , while minimum grain protein was obtained at 400 µg kg -1-of isoproturon (124 mg g -1 ) and atrazine (125 mg g -1 ) application. Among the herbicides tested, atrazine and metribuzin showed a large degree of phytotoxicity to the crop, inhibiting its vegetative growth and was thus incompatible with greengram. @JASEM