Postnatal changes in hepatic microsomal enzyme activities in the puppy

Area of Science:

• Pharmacology
• Biochemistry
• Veterinary Medicine

Background:

• Enzyme activity in neonatal animals differs significantly from adults.
• Understanding drug metabolism and detoxification pathways in developing canines is crucial for veterinary pharmacology.

Purpose of the Study:

• To investigate the developmental changes in key liver enzymes (P-450, G6P, GT) in puppies from birth to adulthood.
• To assess the impact of phenobarbital on these enzymes in young puppies.

Main Methods:

• In vitro assays of glucose-6-phosphatase (G6P), UDP-glucuronyl transferase (GT), and P-450 in liver homogenates from puppies (0-42 days) and adult dogs.
• Enzyme activity measurements using native and activated forms.
• Analysis of liver protein and water content.
• Phenobarbital induction study in 8- to 13-day-old puppies.

Main Results:

• All measured enzyme activities (P-450, G6P, GT) showed age-related increases from birth to 42 days.
• Enzyme activities expressed per unit of wet or dried liver weight differed between puppies and adults due to variations in water content.
• Phenobarbital administration induced P-450 and bilirubin GT activity, but decreased G6P activity, with no significant effect on p-nitrophenol GT in young puppies.
• Evidence suggests two functionally distinct GTs for bilirubin and p-nitrophenol conjugation in dogs.

Conclusions:

• Liver enzyme systems (P-450, G6P, GT) in puppies are immature at birth and mature during postnatal development.
• Drug metabolism capacity in puppies differs from adults and can be modulated by specific agents like phenobarbital.
• The dog liver likely possesses distinct UDP-glucuronyl transferases for different substrates.