Photic regulation of heme oxygenase activity in the golden hamster retina: involvement of dopamine

Abstract

The photic regulation of heme oxygenase (HO) activity was examined in the golden hamster retina. This enzymatic activity was significantly higher at midday than at midnight. When the hamsters were placed under constant darkness for 48 h and killed at subjective day or at subjective night, the differences in HO activity disappeared. Western blot analysis showed no differences in HO levels among these time points. Dopamine significantly increased this activity in retinas excised at noon or at midnight, with a higher sensitivity at night. The effect of dopamine was reversed by SCH 23390 but not by spiperone and clozapine and it was not reproduced by quinpirole. In vitro, the increase in HO activity found in retinas incubated under light for 1 h was significantly reduced by SCH 23390. Two cAMP analogs increased HO activity and their effect, as well as the effect of dopamine was blocked by H-89, a protein kinase A (PKA) inhibitor. Tin protoporphyrin IX, an HO inhibitor, significantly decreased cGMP accumulation with maximal effects during the day. Low concentrations of bilirubin decreased retinal thiobarbituric acid substances levels (an index of lipid peroxidation) in basal conditions and after exposing retinal cells to H 2 O 2 . These results suggest that hamster retinal HO activity is regulated by the photic stimulus, probably through a dopamine/cAMP/PKA dependent pathway.

The influence of light and darkness on cutaneous fluorescence in mice

“…Recently, a photic regulation mechanism of haem oxygenase (HO), the enzyme that oxidizes haem into biliverdin, CO and ferrous iron, was reported [27]. The activity of HO in hamster retina changes according to light-dark cycles, being highest at midday [27]. This means that the haem turnover is faster during the daytime, which is in agreement with our findings showing lower porphyrin levels in skin exposed to daylight.…”

“…Recently, a photic regulation mechanism of haem oxygenase (HO), the enzyme that oxidizes haem into biliverdin, CO and ferrous iron, was reported [27]. The activity of HO in hamster retina changes according to light-dark cycles, being highest at midday [27].…”

Effects of heme oxygenase isozymes on Leydig cells steroidogenesis

“…Transcriptional activation of the Ho-1 gene via the PKA-signaling pathway has been demonstrated in rat hepatocyte cultures and vascular smooth muscle (Durante et al 1997, Immenschuh et al 1998). It has also been shown that HO-2 isozyme, which is constitutively expressed, can be induced by different factors (Liu et al 2000, Tschugguel et al 2001, Sacca et al 2003. In this work, we have demonstrated that both HO-1 and HO-2 protein levels were increased by hCG or db-cAMP in MA-10 cells, indicating the involvement of cAMP/PKA signal transduction pathway in this mechanism.…”

“…While HO-1 (32 kDa) expression can be induced by its own substrate heme, and several other stress stimuli such as heavy metals, lipopolysaccharide (LPS), inflammatory mediators, and oxidized low-density proteins (Otterbein & Choi 2000), the other two isoforms, HO-2 (36 kDa) and , are constitutively expressed (McCoubrey et al 1992(McCoubrey et al , 1997. However, recent studies have shown that corticosterone, estradiol, and a photic signal can induce HO-2 expression in testis (Liu et al 2000), endothelial cells (Tschugguel et al 2001), and retina (Sacca et al 2003) respectively. Both HO-1 and HO-2 isoforms have been detected in diverse organs, including reproductive ones such as testes (Trakshel & Maines 1988, Ewing & Maines 1995, placenta (Lyall et al 2000), uterus (Acevedo & Ahmed 1998), and ovary (Alexandreanu & Lawson 2003).…”

Light Pulse‐Induced Heme and Iron‐Associated Transcripts in Mouse Brain: A Microarray Analysis

“…These same regions of the forebrain exhibit enhanced expression of the gene for heme oxygenase 2 (Hmox2), an enzyme that generates CO using heme as a substrate (Vincent et al, 1994). Photic regulation of Hmox2 enzymatic activity was also found in hamster retina, where under LD conditions activity was significantly higher at mid-day than at midnight (Sacca et al, 2003). In DD, however, these differences disappeared.…”